genksyms: drop *.hash.c from .gitignore

This is a left-over of commit bb3290d916 ("Remove gperf usage from
toolchain").

We do not generate a hash function any more.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/genksyms/.gitignore

@@ -1,4 +1,3 @@
-*.hash.c
 *.lex.c
 *.tab.c
 *.tab.h