gdb/testsuite: rename .py.in files to .py

I noticed these files because they weren't considered by black for
reformatting, prior to adding pyproject.toml, because their extension is
not .py.  I don't think they specifically need to be named .py.in, so I
suggest renaming them to .py.  This will make it nicer to edit them, as
editors will recognize them more easily as Python files.

Perhaps this was needed before, when the testsuite didn't always put
output files in the output directory.  Then, a different name for the
source and destination file might have been desirable to avoid
overwriting a file with itself (perhaps that wasn't well handled).  But
in any case, it doesn't see to cause any problem now.

gdb/testsuite/ChangeLog:

	* gdb.python/py-framefilter-gdb.py.in: Rename to:
	* gdb.python/py-framefilter-gdb.py: ... this.
	* gdb.python/py-framefilter-invalidarg-gdb.py.in: Rename to:
	* gdb.python/py-framefilter-invalidarg-gdb.py: ... this.

Change-Id: I63bb94010bbbc33434ee1c91a386c91fc1ff80bc