[ELF] - Depricate version references.

This is PR28358

According to
https://www.akkadia.org/drepper/dsohowto.pdf

"The fourth point, the VERS 1.0 version being referred to in the VERS 2.0 definition, is not really important in symbol versioning. It marks the predecessor relationship of the two versions and it is done to maintain the similar- ities with Solaris’ internal versioning. It does not cause any problem it might in fact be useful to a human reader so predecessors should always be mentioned."

Patch partially reverts 273423 "[ELF] - Implemented version script hierarchies.",
version references are just ignored now.

Differential revision: http://reviews.llvm.org/D21888

llvm-svn: 274345