Move format's onBegin just before team preview
Move format's onBegin just before team preview

Since team length validation is now handled automatically from declarative
format data, the onBegin hook has became rather useless.

This gives it a niche by allowing it to dynamically customize teams, as
required by some approved Other Metas.

Syurra/Pokemon-Showdown,sirDonovan/Pokemon-Showdown,AustinXII/Pokemon-Showdown,TheManwithskills/Creature-phil-boiler,svivian/Pokemon-Showdown,Nineage/Origin,TheFenderStory/Showdown-Boilerplate,Firestatics/Omega-Alpha,Firestatics/omega,TheFenderStory/Pokemon-Showdown,urkerab/Pokemon-Showdown,KewlStatics/Showdown-Template,Enigami/Pokemon-Showdown,urkerab/Pokemon-Showdown,DarkSuicune/Pokemon-Showdown,panpawn/Pokemon-Showdown,Lord-Haji/SpacialGaze,psnsVGC/Wish-Server,ShowdownHelper/Saffron,cadaeic/Pokemon-Showdown,kotarou3/Krister-Pokemon-Showdown,xCrystal/Pokemon-Showdown,Wando94/Spite,svivian/Pokemon-Showdown,HoeenCoder/SpacialGaze,svivian/Pokemon-Showdown,xfix/Pokemon-Showdown,svivian/Pokemon-Showdown,TheManwithskills/COC,Lauc1an/Perulink-Showdown,EienSeiryuu/Pokemon-Showdown,sirDonovan/Pokemon-Showdown,KewlStatics/Pokeindia-Codes,AWailOfATail/Pokemon-Showdown,ehk12/coregit,Vacate/Pokemon-Showdown,Pikachuun/Pokemon-Showdown-SMCMDM,QuiteQuiet/Pokemon-Showdown,Kokonoe-san/Glacia-PS,Lord-Haji/SpacialGaze,ehk12/coregit,aakashrajput/Pokemon-Showdown,TheManwithskills/DS,xfix/Pokemon-Showdown,panpawn/Gold-Server,Enigami/Pokemon-Showdown,Sora-League/Sora,Mystifi/Exiled,CreaturePhil/Showdown-Boilerplate,CreaturePhil/Showdown-Boilerplate,Bryan-0/Pokemon-Showdown,SSJGVegito007/Vegito-s-Server,yashagl/yash-showdown,azum4roll/Pokemon-Showdown,Mystifi/Exiled,Nineage/Origin,Lord-Haji/SpacialGaze,PS-Spectral/Spectral,xCrystal/Pokemon-Showdown,Mystifi/Exiled,KewlStatics/Shit,Zarel/Pokemon-Showdown,kuroscafe/Showdown-Boilerplate,PS-Spectral/Spectral,Enigami/Pokemon-Showdown,aakashrajput/Pokemon-Showdown,SolarisFox/Pokemon-Showdown,HoeenCoder/SpacialGaze,Pikachuun/Pokemon-Showdown,BlazingAura/Showdown-Boilerplate,cadaeic/Pokemon-Showdown,DesoGit/Tsunami_PS,ZestOfLife/PSserver,HoeenCoder/SpacialGaze,danpantry/Pokemon-Showdown,DarkSuicune/Pokemon-Showdown,BlazingAura/Showdown-Boilerplate,Irraquated/Pokemon-Showdown,Kokonoe-san/Glacia-PS,TheManwithskills/COC,KewlStatics/Shit,EienSeiryuu/Pokemon-Showdown,TheFenderStory/Showdown-Boilerplate,DesoGit/TsunamiPS,yashagl/pokemon-showdown,sirDonovan/Pokemon-Showdown,SSJGVegito007/Vegito-s-Server,Alpha-Devs/OmegaRuby-Server,jd4564/Pokemon-Showdown,Pikachuun/Pokemon-Showdown,TheFenderStory/Pokemon-Showdown,yashagl/yash-showdown,jd4564/Pokemon-Showdown,TbirdClanWish/Pokemon-Showdown,KewlStatics/Showdown-Template,AbsolitoSweep/Absol-server,AbsolitoSweep/Absol-server,Zarel/Pokemon-Showdown,CharizardtheFireMage/Showdown-Boilerplate,panpawn/Pokemon-Showdown,psnsVGC/Wish-Server,xfix/Pokemon-Showdown,Volcos/SpacialGaze,urkerab/Pokemon-Showdown,ZestOfLife/FestiveLife,QuiteQuiet/Pokemon-Showdown,danpantry/Pokemon-Showdown,Alpha-Devs/Alpha-Server,CharizardtheFireMage/Showdown-Boilerplate,arkanox/MistShowdown,kuroscafe/Showdown-Boilerplate,SolarisFox/Pokemon-Showdown,Volcos/SpacialGaze,Lauc1an/Perulink-Showdown,ZestOfLife/PSserver,ShowdownHelper/Saffron,Wando94/Spite,Guernouille/Pokemon-Showdown,ZestOfLife/FestiveLife,Bryan-0/Pokemon-Showdown,Irraquated/Pokemon-Showdown,Firestatics/Omega-Alpha,TheManwithskills/Creature-phil-boiler,Zarel/Pokemon-Showdown,Guernouille/Pokemon-Showdown,DesoGit/Tsunami_PS,AWailOfATail/Pokemon-Showdown,svivian/Pokemon-Showdown,kotarou3/Krister-Pokemon-Showdown,SkyeTheFemaleSylveon/Pokemon-Showdown,Alpha-Devs/OmegaRuby-Server,HoeenCoder/SpacialGaze,AustinXII/Pokemon-Showdown,AustinXII/Pokemon-Showdown,AnaRitaTorres/Pokemon-Showdown,xCrystal/Pokemon-Showdown,panpawn/Gold-Server,jumbowhales/Pokemon-Showdown,PS-Spectral/Spectral,azum4roll/Pokemon-Showdown,Firestatics/omega,panpawn/Gold-Server,xfix/Pokemon-Showdown,Flareninja/Showdown-Boilerplate,kuroscafe/Paradox,DesoGit/TsunamiPS,AWailOfATail/Pokemon-Showdown,yashagl/pokemon-showdown,Git-Worm/City-PS,AnaRitaTorres/Pokemon-Showdown,jumbowhales/Pokemon-Showdown,DesoGit/Tsunami_PS,Alpha-Devs/Alpha-Server,Syurra/Pokemon-Showdown,arkanox/MistShowdown,jumbowhales/Pokemon-Showdown,KewlStatics/Alliance,KewlStatics/Pokeindia-Codes,Elveman/RPCShowdownServer,CreaturePhil/Showdown-Boilerplate,Ecuacion/Pokemon-Showdown,TbirdClanWish/Pokemon-Showdown,aakashrajput/Pokemon-Showdown,KewlStatics/Alliance,Git-Worm/City-PS,Ecuacion/Pokemon-Showdown,QuiteQuiet/Pokemon-Showdown,Flareninja/Showdown-Boilerplate,Vacate/Pokemon-Showdown,SkyeTheFemaleSylveon/Pokemon-Showdown,Hidden-Mia/Roleplay-PS,TheManwithskills/DS,Irraquated/Pokemon-Showdown,Sora-League/Sora,zek7rom/SpacialGaze,xfix/Pokemon-Showdown,Elveman/RPCShowdownServer,zek7rom/SpacialGaze,kuroscafe/Paradox,ShowdownHelper/Saffron,Pikachuun/Pokemon-Showdown-SMCMDM,Hidden-Mia/Roleplay-PS,Enigami/Pokemon-Showdown,Sora-League/Sora