Revert "[ELF2] - Implemented rel[a].plt sections"

This reverts commit r249816.

It broke building llvm with lld:

$ ./bin/FileCheck
./bin/FileCheck: error while loading shared libraries: unexpected PLT reloc type 0x06

I think the only thing that is wrong with this patch is that it is too soon.

The plt we create (and its relocs) don't support lazy loading, so they have
to be relocated as ordinary dynamic relocations.

llvm-svn: 249835