[llvm-readelf/obj] - Refine the implementation of `printGNUVersionSectionProlog`

This:
1) Changes its signature.
2) Refines the name of local variable (`SymTabName`->`LinkedSecName`,
   because SHT_GNU_verneed/SHT_GNU_verdef are linked with the string table, not with the symbol table).
3) Stops using the `unwrapOrError` inside.

Differential revision: https://reviews.llvm.org/D91964