Remove kindInGroup reference.

That kind of reference was used only in ELFFile, and the use of
that reference there didn't seem to make sense. All test still
pass (after adjusting symbol names) without that code. LLD is
still be able to link LLD and Clang. Looks like we just don't
need this.

http://reviews.llvm.org/D7189

llvm-svn: 227259