genksyms: fix stale comment

(shipped source) is a stale comment.

Since commit 833e622459 ("genksyms: generate lexer and parser during
build instead of shipping"), there is no source file to be shipped in
this directory.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/genksyms/Makefile

@@ -22,7 +22,7 @@ $(obj)/pars%.tab.c $(obj)/pars%.tab.h: $(src)/pars%.y FORCE
 
 endif
 
-# -I needed for generated C source (shipped source)
+# -I needed for generated C source to include headers in source tree
 HOSTCFLAGS_parse.tab.o := -I $(srctree)/$(src)
 HOSTCFLAGS_lex.lex.o := -I $(srctree)/$(src)