[ELF] Remove checking for spurious '@' at the end of dynamic sym names

llvm-readobj currently has a bug (see PR40097) where it prints '@' at
the end of unversioned dynamic symbols. This bug will be fixed in a
separate later commit, but these tests need fixing first.

Reviewed by: ruiu, Higuoxing

Differential Revision: https://reviews.llvm.org/D56388

llvm-svn: 350614