Revert "autoconf: Fix soname for libLLVM-Major.Minor.so"

This reverts commit r208708.

I forgot to run make clean before testing this and it broke tools
linking.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208709 91177308-0d34-0410-b5e6-96231b3b80d8