[llvm-readobj] - Don't get the name of the symbol table in ELFDumper<ELFT>::printSymb...

[llvm-readobj] - Don't get the name of the symbol table in ELFDumper<ELFT>::printSymbolsHelper.

It was requested in D84173 thread to not do it, because otherwise we extract and
check the name of the symbol table in LLVM style, but do not use it and
might report a warning which perhaps might be confusing.

Differential revision: https://reviews.llvm.org/D84231