r354605 moved LLD to the unified revision handling introduced in
rL353268 / r352729 and removed uses of LLD_REPOSITORY_STRING and
LLD_REVISION_STRING.
After this change, we no longer compute the (now-unused) values
of these two variables.
Since this removes the only use of llvm/utils/GetRepositoryPath,
remove that too (it's redundant with the system added in r354605).
While here, also remove LLD_VERSION_MAJOR and LLD_VERSION_MINOR.
Their uses were removed in r285163.
Also remove LLD_VERSION from Version.inc which as far as I can
tell has been unused since the file was added in r219277.
No behavior change.