Revert "[clangd] Enable lit internal shell by default"

This reverts commit c51c382.

This breaks at least one buildbot:
1. https://lab.llvm.org/buildbot/#/builders/134/builds/30460

Author: boomanaiden154

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

@@ -1,26 +1,13 @@
-import os
-
 import lit.llvm
 
 lit.llvm.initialize(lit_config, config)
 lit.llvm.llvm_config.clang_setup()
 lit.llvm.llvm_config.use_default_substitutions()
 
-# TODO: Consolidate the logic for turning on the internal shell by default for all LLVM test suites.
-# See https://github.com/llvm/llvm-project/issues/106636 for more details.
-#
-# We prefer the lit internal shell which provides a better user experience on failures
-# and is faster unless the user explicitly disables it with LIT_USE_INTERNAL_SHELL=0
-# env var.
-use_lit_shell = True
-lit_shell_env = os.environ.get("LIT_USE_INTERNAL_SHELL")
-if lit_shell_env:
-    use_lit_shell = lit.util.pythonize_bool(lit_shell_env)
-
 config.name = "Clangd"
 config.suffixes = [".test"]
 config.excludes = ["Inputs"]
-config.test_format = lit.formats.ShTest(not use_lit_shell)
+config.test_format = lit.formats.ShTest(not lit.llvm.llvm_config.use_lit_shell)
 config.test_source_root = config.clangd_source_dir + "/test"
 config.test_exec_root = config.clangd_binary_dir + "/test"