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

arch/powerpc/boot/.gitignore

 addnote
 empty.c
 hack-coff
-infblock.c
-infblock.h
-infcodes.c
-infcodes.h
 inffast.c
 inffast.h
 inffixed.h