Revert "[lldb] Calculate relative path for symbol links"

This reverts commit 958091c2.

This commit incorrectly sets the _lldb.so symlink (at least it does when
building in Stefans' two build directory mode, where you build llvm with
cmake/ninja and lldb with cmake/Xcode, using a cmake generated project.

The _lldb.so link is SUPPOSED to point to:

bin/LLDB.framework/Versions/A/LLDB

but instead it points to

bin/LLDB

which is where LLDB was staged to before constructing the framework.  This
causes all sorts of problems when we then build the lldb driver into bin -
remember that MacOS is a case-preserving but case insensitive filesystem -
so when we later go to dlopen _lldb.so, we dlopen the main executable instead.

llvm-svn: 374226