kconfig: omit --oldaskconfig option for 'make config'

scripts/kconfig/conf.c line 39 defines the default of input_mode as
oldaskconfig. Hence, 'make config' works in the same way even without
the --oldaskconfig option given. Note this in the help message.

This will be helpful to unify build rules in Makefile in the next
commit.
Signed-off-by: NMasahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/Makefile

@@ -29,7 +29,7 @@ menuconfig: $(obj)/mconf
 	$(Q)$< $(silent) $(Kconfig)
 
 config: $(obj)/conf
-	$(Q)$< $(silent) --oldaskconfig $(Kconfig)
+	$(Q)$< $(silent) $(Kconfig)
 
 nconfig: $(obj)/nconf
 	$(Q)$< $(silent) $(Kconfig)

scripts/kconfig/conf.c

@@ -483,6 +483,7 @@ static void conf_usage(const char *progname)
 	printf("  --randconfig            New config with random answer to all options\n");
 	printf("  --yes2modconfig         Change answers from yes to mod if possible\n");
 	printf("  --mod2yesconfig         Change answers from mod to yes if possible\n");
+	printf("  (If none of the above is given, --oldaskconfig is the default)\n");
 }
 
 int main(int ac, char **av)