kconfig: localmodconfig: remove unused $config

This is unused since commit cdfc47950a ("kconfig: search for a config
to base the local(mod|yes)config on").

Having unused $config is confusing because $config is used as a local
variable in various sub-routines.

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

scripts/kconfig/streamline_config.pl

@@ -56,8 +56,6 @@ sub dprint {
     print STDERR @_;
 }
 
-my $config = ".config";
-
 my $uname = `uname -r`;
 chomp $uname;