Style improvements in gdb/python

This fixes a few minor style issues I found in gdb/python: some
unnecessary casts, the removal of an unnecessary local variable, and
one instance of incorrect formatting.

Tested by rebuilding and re-running gdb.python.

gdb/ChangeLog
2019-01-02  Tom Tromey  <tom@tromey.com>

	* python/py-inferior.c (gdbpy_initialize_inferior): Fix
	indentation.
	* python/py-frame.c (frapy_older): Remove cast.
	(frapy_newer): Likewise.
	* python/py-breakpoint.c (local_setattro): Remove cast.
	* python/py-arch.c (archpy_name): Remove local variable.
	* python/py-type.c (gdbpy_lookup_type): Remove cast.