remove pointless, unused typing-only import in the test runner

In the commit that originally added this import, it wasn't even used.
Now the implementation is being moved, so it will fail to work.

I do not know why I originally added it, but it needs to go. :)

run_project_tests.py

@@ -63,7 +63,6 @@ if T.TYPE_CHECKING:
     from mesonbuild.environment import Environment
     from mesonbuild._typing import Protocol
     from concurrent.futures import Future
-    from mesonbuild.modules.python import PythonIntrospectionDict
 
     class CompilerArgumentType(Protocol):
         cross_file: str