Remove the "prep" option from the public API of dsolve()
Remove the "prep" option from the public API of dsolve()

See the discussion at
https://groups.google.com/d/topic/sympy/kl_j_xt1ZXI/discussion.

abhiii5459/sympy,Titan-C/sympy,Curious72/sympy,wanglongqi/sympy,drufat/sympy,Shaswat27/sympy,atreyv/sympy,iamutkarshtiwari/sympy,lindsayad/sympy,liangjiaxing/sympy,skidzo/sympy,chaffra/sympy,VaibhavAgarwalVA/sympy,emon10005/sympy,MechCoder/sympy,Vishluck/sympy,MridulS/sympy,yashsharan/sympy,grevutiu-gabriel/sympy,meghana1995/sympy,cccfran/sympy,jerli/sympy,MridulS/sympy,kumarkrishna/sympy,madan96/sympy,abloomston/sympy,yashsharan/sympy,sampadsaha5/sympy,iamutkarshtiwari/sympy,wanglongqi/sympy,MridulS/sympy,Mitchkoens/sympy,sunny94/temp,Gadal/sympy,jerli/sympy,drufat/sympy,ga7g08/sympy,dqnykamp/sympy,pbrady/sympy,shikil/sympy,skidzo/sympy,madan96/sympy,skirpichev/omg,farhaanbukhsh/sympy,jbbskinny/sympy,Titan-C/sympy,asm666/sympy,vipulroxx/sympy,kumarkrishna/sympy,hrashk/sympy,bukzor/sympy,abloomston/sympy,postvakje/sympy,kaichogami/sympy,rahuldan/sympy,sahilshekhawat/sympy,sahilshekhawat/sympy,kmacinnis/sympy,moble/sympy,Shaswat27/sympy,debugger22/sympy,jbbskinny/sympy,Sumith1896/sympy,kmacinnis/sympy,debugger22/sympy,ahhda/sympy,Designist/sympy,Arafatk/sympy,ahhda/sympy,dqnykamp/sympy,hargup/sympy,garvitr/sympy,jerli/sympy,saurabhjn76/sympy,aktech/sympy,Mitchkoens/sympy,cccfran/sympy,kevalds51/sympy,vipulroxx/sympy,kevalds51/sympy,toolforger/sympy,Sumith1896/sympy,emon10005/sympy,mcdaniel67/sympy,saurabhjn76/sympy,wyom/sympy,madan96/sympy,rahuldan/sympy,oliverlee/sympy,Gadal/sympy,Mitchkoens/sympy,mafiya69/sympy,iamutkarshtiwari/sympy,yukoba/sympy,Designist/sympy,ChristinaZografou/sympy,Sumith1896/sympy,cccfran/sympy,souravsingh/sympy,pandeyadarsh/sympy,asm666/sympy,ChristinaZografou/sympy,AunShiLord/sympy,jaimahajan1997/sympy,atreyv/sympy,Shaswat27/sympy,toolforger/sympy,kaushik94/sympy,sampadsaha5/sympy,chaffra/sympy,lidavidm/sympy,wyom/sympy,lidavidm/sympy,pandeyadarsh/sympy,ga7g08/sympy,amitjamadagni/sympy,kevalds51/sympy,hrashk/sympy,shikil/sympy,bukzor/sympy,rahuldan/sympy,meghana1995/sympy,lindsayad/sympy,skidzo/sympy,atreyv/sympy,beni55/sympy,kaushik94/sympy,amitjamadagni/sympy,aktech/sympy,yukoba/sympy,lidavidm/sympy,kaushik94/sympy,shipci/sympy,moble/sympy,farhaanbukhsh/sympy,AkademieOlympia/sympy,meghana1995/sympy,pandeyadarsh/sympy,kmacinnis/sympy,VaibhavAgarwalVA/sympy,beni55/sympy,lindsayad/sympy,shikil/sympy,atsao72/sympy,bukzor/sympy,ahhda/sympy,MechCoder/sympy,AunShiLord/sympy,Vishluck/sympy,yashsharan/sympy,dqnykamp/sympy,beni55/sympy,ChristinaZografou/sympy,AkademieOlympia/sympy,jamesblunt/sympy,maniteja123/sympy,sahmed95/sympy,Arafatk/sympy,Davidjohnwilson/sympy,abloomston/sympy,Davidjohnwilson/sympy,sahilshekhawat/sympy,souravsingh/sympy,kaichogami/sympy,hargup/sympy,kaichogami/sympy,jamesblunt/sympy,kumarkrishna/sympy,asm666/sympy,maniteja123/sympy,Arafatk/sympy,mafiya69/sympy,abhiii5459/sympy,garvitr/sympy,vipulroxx/sympy,liangjiaxing/sympy,mcdaniel67/sympy,cswiercz/sympy,pbrady/sympy,aktech/sympy,diofant/diofant,wanglongqi/sympy,Gadal/sympy,AkademieOlympia/sympy,mcdaniel67/sympy,jamesblunt/sympy,drufat/sympy,garvitr/sympy,sunny94/temp,ga7g08/sympy,Curious72/sympy,souravsingh/sympy,atsao72/sympy,maniteja123/sympy,grevutiu-gabriel/sympy,Designist/sympy,toolforger/sympy,saurabhjn76/sympy,MechCoder/sympy,postvakje/sympy,grevutiu-gabriel/sympy,liangjiaxing/sympy,abhiii5459/sympy,cswiercz/sympy,hargup/sympy,mafiya69/sympy,jbbskinny/sympy,shipci/sympy,emon10005/sympy,debugger22/sympy,jaimahajan1997/sympy,Titan-C/sympy,hrashk/sympy,sahmed95/sympy,postvakje/sympy,moble/sympy,oliverlee/sympy,sunny94/temp,farhaanbukhsh/sympy,wyom/sympy,Davidjohnwilson/sympy,Curious72/sympy,sampadsaha5/sympy,AunShiLord/sympy,cswiercz/sympy,chaffra/sympy,shipci/sympy,atsao72/sympy,pbrady/sympy,sahmed95/sympy,yukoba/sympy,Vishluck/sympy,oliverlee/sympy,jaimahajan1997/sympy,VaibhavAgarwalVA/sympy