Blackfin: drop unneeded asm/.gitignore

We don't create a include/asm/mach/ symlink anymore, so we don't need the
.gitignore for it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/include/asm/.gitignore

@@ -1 +0,0 @@
-+mach