[CodeGen] Update hasSideEffects comment. NFC.
[CodeGen] Update hasSideEffects comment. NFC.

We used to have 3 side effect flags, but as of r222809, we only have
hasSideEffects.  Change the comment to reflect that.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@298220 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit e80b226a1261f98aa4f1f596e5e216ec24f91f8a)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm