[lit] Remove clang_libs_dir

Seems to have been added accidentally in 58db03a116 and then
copied into clangd by me (but not actually needed).

clang-tools-extra/clangd/test/lit.site.cfg.py.in

@@ -2,7 +2,6 @@
 
 # Variables needed for common clang config.
 config.lit_tools_dir = "@LLVM_LIT_TOOLS_DIR@"
-config.clang_libs_dir = "@CLANG_LIBS_DIR@"
 config.target_triple = "@LLVM_TARGET_TRIPLE@"
 config.host_triple = "@LLVM_HOST_TRIPLE@"
 config.python_executable = "@Python3_EXECUTABLE@"

llvm/utils/lit/lit/llvm/config.py

@@ -489,7 +489,6 @@ class LLVMConfig(object):
 
         lib_dir_props = [
             self.config.name.lower() + '_libs_dir',
-            'clang_libs_dir',
             'llvm_shlib_dir',
             'llvm_libs_dir',
             ]