[ELF] Delete GotEntrySize and GotPltEntrySize

GotEntrySize and GotPltEntrySize were added in D22288. Later, with
the introduction of wordsize() (then Config->Wordsize), they become
redundant, because there is no target that sets GotEntrySize or
GotPltEntrySize to a number different from Config->Wordsize.

Reviewed By: grimar, ruiu

Differential Revision: https://reviews.llvm.org/D62727

llvm-svn: 362220