Disable parse_headers when generating commands

[keith]

Since the parse_headers action has a command line with no source files
and only headers it results in an exception like:

  File "/home/ubuntu/.cache/bazel/_bazel_ubuntu/480ee760ab026be301955dc1adc19e40/execroot/_main/bazel-out/k8-dbg/bin/bazel/internal/internal_refresh_compile_commands_use_script_instead.runfiles/_main/bazel/internal/internal_refresh_compile_commands_use_script_instead.py", line 1087, in _get_cpp_command_for_files
    source_files, header_files = _get_files(compile_action, bazel_binary)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/.cache/bazel/_bazel_ubuntu/480ee760ab026be301955dc1adc19e40/execroot/_main/bazel-out/k8-dbg/bin/bazel/internal/internal_refresh_compile_commands_use_script_instead.runfiles/_main/bazel/internal/internal_refresh_compile_commands_use_script_instead.py", line 590, in _get_files
    assert source_file_candidates, f"No source files found in compile args: {compile_action.arguments}.\nPlease file an issue with this information!"
           ^^^^^^^^^^^^^^^^^^^^^^

This header knowledge probably isn't necessary anyways since that can
come from other sources.