libLTO.{so,dylib}: remove unused non-LTO symbols

These dissembler symbols are not used by LTO (see Apple ld64's use
in check-llvm-tools-lto). On ELF platforms, these symbols are not defined and are
rejected by ld --no-undefined-version.

I think this is a more proper solution than D139932 and this fixes
-DBUILD_SHARED_LIBS=on for ELF as well.