[lldb] Update hardcoded Makefile.rules inclusions.

This replaces `include $(LEVEL)/Makefile.rules` with `include Makefile.rules`.
The lldb test driver already passes the include path when running make, and specifically looking for "../../Makefile.rules" forces the test to be in a specific location.
Removing this hardcoded relative path will make it possible to move this test as-is.