Remove ExprCondPair.is_commutative.
Remove ExprCondPair.is_commutative.

ExprCondPair is a Tuple, and commutativity doesn't make sense for Tuples
since they can't be multiplied.

Add implementation of Piecewise.is_commutative

Vishluck/sympy,Shaswat27/sympy,oliverlee/sympy,lidavidm/sympy,shikil/sympy,pbrady/sympy,jamesblunt/sympy,kmacinnis/sympy,atreyv/sympy,grevutiu-gabriel/sympy,wyom/sympy,kaushik94/sympy,shikil/sympy,beni55/sympy,yukoba/sympy,AunShiLord/sympy,Sumith1896/sympy,Shaswat27/sympy,cswiercz/sympy,amitjamadagni/sympy,jerli/sympy,meghana1995/sympy,lidavidm/sympy,ga7g08/sympy,vipulroxx/sympy,shipci/sympy,ahhda/sympy,chaffra/sympy,AkademieOlympia/sympy,pbrady/sympy,saurabhjn76/sympy,beni55/sympy,kaichogami/sympy,postvakje/sympy,hrashk/sympy,skidzo/sympy,Curious72/sympy,amitjamadagni/sympy,sunny94/temp,drufat/sympy,jaimahajan1997/sympy,ahhda/sympy,asm666/sympy,VaibhavAgarwalVA/sympy,MridulS/sympy,mcdaniel67/sympy,mafiya69/sympy,toolforger/sympy,AunShiLord/sympy,dqnykamp/sympy,atsao72/sympy,kevalds51/sympy,wanglongqi/sympy,liangjiaxing/sympy,jbbskinny/sympy,mafiya69/sympy,shipci/sympy,Designist/sympy,ChristinaZografou/sympy,hrashk/sympy,Davidjohnwilson/sympy,toolforger/sympy,lindsayad/sympy,ChristinaZografou/sympy,cswiercz/sympy,sahilshekhawat/sympy,cccfran/sympy,lindsayad/sympy,debugger22/sympy,VaibhavAgarwalVA/sympy,madan96/sympy,Mitchkoens/sympy,sampadsaha5/sympy,oliverlee/sympy,lidavidm/sympy,hrashk/sympy,kaichogami/sympy,jbbskinny/sympy,mafiya69/sympy,vipulroxx/sympy,moble/sympy,kumarkrishna/sympy,Davidjohnwilson/sympy,jaimahajan1997/sympy,meghana1995/sympy,grevutiu-gabriel/sympy,MridulS/sympy,liangjiaxing/sympy,AkademieOlympia/sympy,madan96/sympy,flacjacket/sympy,emon10005/sympy,yashsharan/sympy,iamutkarshtiwari/sympy,MechCoder/sympy,hargup/sympy,Davidjohnwilson/sympy,wanglongqi/sympy,oliverlee/sympy,jamesblunt/sympy,kmacinnis/sympy,maniteja123/sympy,farhaanbukhsh/sympy,shipci/sympy,emon10005/sympy,asm666/sympy,iamutkarshtiwari/sympy,abloomston/sympy,pandeyadarsh/sympy,bukzor/sympy,wanglongqi/sympy,aktech/sympy,rahuldan/sympy,hargup/sympy,maniteja123/sympy,debugger22/sympy,jbbskinny/sympy,madan96/sympy,wyom/sympy,skidzo/sympy,Titan-C/sympy,chaffra/sympy,postvakje/sympy,Gadal/sympy,bukzor/sympy,Titan-C/sympy,kevalds51/sympy,toolforger/sympy,atreyv/sympy,abloomston/sympy,sunny94/temp,postvakje/sympy,farhaanbukhsh/sympy,kumarkrishna/sympy,rahuldan/sympy,pandeyadarsh/sympy,Arafatk/sympy,emon10005/sympy,jamesblunt/sympy,atsao72/sympy,saurabhjn76/sympy,pbrady/sympy,kaushik94/sympy,MechCoder/sympy,sunny94/temp,sahmed95/sympy,grevutiu-gabriel/sympy,drufat/sympy,sahmed95/sympy,shikil/sympy,kevalds51/sympy,kaushik94/sympy,abhiii5459/sympy,skidzo/sympy,saurabhjn76/sympy,meghana1995/sympy,liangjiaxing/sympy,Sumith1896/sympy,beni55/sympy,moble/sympy,sahilshekhawat/sympy,Vishluck/sympy,Gadal/sympy,diofant/diofant,kaichogami/sympy,yukoba/sympy,abhiii5459/sympy,iamutkarshtiwari/sympy,Designist/sympy,yashsharan/sympy,dqnykamp/sympy,sampadsaha5/sympy,atreyv/sympy,Gadal/sympy,abhiii5459/sympy,yukoba/sympy,yashsharan/sympy,AkademieOlympia/sympy,farhaanbukhsh/sympy,atsao72/sympy,jerli/sympy,Vishluck/sympy,cccfran/sympy,Mitchkoens/sympy,abloomston/sympy,garvitr/sympy,mcdaniel67/sympy,drufat/sympy,garvitr/sympy,cccfran/sympy,hargup/sympy,maniteja123/sympy,mcdaniel67/sympy,rahuldan/sympy,skirpichev/omg,bukzor/sympy,jerli/sympy,Sumith1896/sympy,VaibhavAgarwalVA/sympy,Arafatk/sympy,Arafatk/sympy,chaffra/sympy,debugger22/sympy,kumarkrishna/sympy,MridulS/sympy,sahilshekhawat/sympy,garvitr/sympy,souravsingh/sympy,sahmed95/sympy,ga7g08/sympy,aktech/sympy,wyom/sympy,ahhda/sympy,jaimahajan1997/sympy,srjoglekar246/sympy,ChristinaZografou/sympy,asm666/sympy,MechCoder/sympy,dqnykamp/sympy,pandeyadarsh/sympy,kmacinnis/sympy,sampadsaha5/sympy,aktech/sympy,Designist/sympy,Shaswat27/sympy,souravsingh/sympy,AunShiLord/sympy,moble/sympy,Curious72/sympy,Curious72/sympy,vipulroxx/sympy,ga7g08/sympy,Titan-C/sympy,souravsingh/sympy,cswiercz/sympy,lindsayad/sympy,Mitchkoens/sympy