[AsmParser] Hash is not a comment on some targets

The '#' token is not a comment for all targets (on ARM and AArch64 it marks an
immediate operand), so we shouldn't treat it as such.

Comments are already converted to AsmToken::EndOfStatement by
AsmLexer::LexLineComment, so this check was unnecessary.

Differential Revision: https://reviews.llvm.org/D36405

llvm-svn: 310457