[javascript mode] Remove duplicated extends keyword
[javascript mode] Remove duplicated extends keyword

Closes #3667

namin/CodeMirror,hackmdio/CodeMirror,InternetGuru/CodeMirror,bfrohs/CodeMirror,ashmind/CodeMirror,dperetti/CodeMirror,hackmdio/CodeMirror,Jisuanke/CodeMirror,sourcelair/CodeMirror,rrandom/CodeMirror,xeronith/CodeMirror,wingify/CodeMirror,adobe/CodeMirror2,Dominator008/CodeMirror,TDaglis/CodeMirror,SidPresse/CodeMirror,namin/CodeMirror,grzegorzmazur/CodeMirror,adobe/CodeMirror2,MarcelGerber/CodeMirror,Dominator008/CodeMirror,rrandom/CodeMirror,alur/CodeMirror,hccampos/CodeMirror,kerabromsmu/CodeMirror,jayaprabhakar/CodeMirror,mihailik/CodeMirror,ejgallego/CodeMirror,antimatter15/CodeMirror,codio/CodeMirror,jkaplon/CodeMirror,sourcelair/CodeMirror,mihailik/CodeMirror,jkaplon/CodeMirror,grzegorzmazur/CodeMirror,hackmdio/CodeMirror,thomasjm/CodeMirror,pabloferz/CodeMirror,dperetti/CodeMirror,MarcelGerber/CodeMirror,mtaran-google/CodeMirror,thomasjm/CodeMirror,agendor/CodeMirror,Dominator008/CodeMirror,nightwing/CodeMirror,Jisuanke/CodeMirror,crazy4chrissi/CodeMirror,TDaglis/CodeMirror,ashmind/CodeMirror,antimatter15/CodeMirror,MarcelGerber/CodeMirror,nightwing/CodeMirror,Jisuanke/CodeMirror,codio/CodeMirror,hccampos/CodeMirror,TDaglis/CodeMirror,notepadqq/CodeMirror,kerabromsmu/CodeMirror,pabloferz/CodeMirror,jayaprabhakar/CodeMirror,ThebingServices/CodeMirror,ThebingServices/CodeMirror,namin/CodeMirror,mizchi/CodeMirror,vincentwoo/CodeMirror,jayaprabhakar/CodeMirror,bfrohs/CodeMirror,ficristo/CodeMirror,adobe/CodeMirror2,schanzer/CodeMirror,pabloferz/CodeMirror,ZombieHippie/CodeMirror,ejgallego/CodeMirror,grzegorzmazur/CodeMirror,SidPresse/CodeMirror,wingify/CodeMirror,INTELOGIE/CodeMirror,sourcelair/CodeMirror,ashmind/CodeMirror,wingify/CodeMirror,mtaran-google/CodeMirror,ficristo/CodeMirror,agendor/CodeMirror,notepadqq/CodeMirror,mihailik/CodeMirror,hccampos/CodeMirror,ejgallego/CodeMirror,INTELOGIE/CodeMirror,mizchi/CodeMirror,ZombieHippie/CodeMirror,alur/CodeMirror,crazy4chrissi/CodeMirror,ficristo/CodeMirror,xeronith/CodeMirror,kerabromsmu/CodeMirror,thomasjm/CodeMirror,SidPresse/CodeMirror,alur/CodeMirror,ThebingServices/CodeMirror,InternetGuru/CodeMirror,agendor/CodeMirror,jkaplon/CodeMirror,InternetGuru/CodeMirror,bfrohs/CodeMirror,schanzer/CodeMirror,ZombieHippie/CodeMirror,mizchi/CodeMirror,INTELOGIE/CodeMirror,antimatter15/CodeMirror,xeronith/CodeMirror,dperetti/CodeMirror,vincentwoo/CodeMirror,codio/CodeMirror,mtaran-google/CodeMirror,nightwing/CodeMirror,crazy4chrissi/CodeMirror,rrandom/CodeMirror,vincentwoo/CodeMirror,notepadqq/CodeMirror,schanzer/CodeMirror