[Parse] Remove redundant check
[Parse] Remove redundant check

We already check this in `Parser::tryLexRegexLiteral`,
and the failure case doesn't make sense here as
we call `discardToken` afterwards.

roambotics/swift,glessard/swift,glessard/swift,glessard/swift,benlangmuir/swift,ahoppen/swift,JGiola/swift,roambotics/swift,benlangmuir/swift,roambotics/swift,ahoppen/swift,JGiola/swift,benlangmuir/swift,ahoppen/swift,benlangmuir/swift,apple/swift,benlangmuir/swift,glessard/swift,ahoppen/swift,JGiola/swift,JGiola/swift,apple/swift,JGiola/swift,roambotics/swift,JGiola/swift,apple/swift,apple/swift,roambotics/swift,apple/swift,roambotics/swift,ahoppen/swift,apple/swift,glessard/swift,ahoppen/swift,glessard/swift,benlangmuir/swift