powerpc: remove four unused files from .gitignore

Commit 4f3865fb ("zlib_inflate: Upgrade
library code to a recent version") removed infblock.c, infblock.h,
infcodes.c, and infcodes.h from the tree. Remove their entries in
powerpc's .gitignore file too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>