kconfig: remove check_stdin()

Except silentoldconfig, valid_stdin is 1, so check_stdin() is no-op.

oldconfig and silentoldconfig work almost in the same way except that
the latter generates additional files under include/.  Both ask users
for input for new symbols.

I do not know why only silentoldconfig requires stdio be tty.

  $ rm -f .config; touch .config
  $ yes "" | make oldconfig > stdout
  $ rm -f .config; touch .config
  $ yes "" | make silentoldconfig > stdout
  make[1]: *** [silentoldconfig] Error 1
  make: *** [silentoldconfig] Error 2
  $ tail -n 4 stdout
  Console input/output is redirected. Run 'make oldconfig' to update configuration.

  scripts/kconfig/Makefile:40: recipe for target 'silentoldconfig' failed
  Makefile:507: recipe for target 'silentoldconfig' failed

Redirection is useful, for example, for testing where we want to give
particular key inputs from a test file, then check the result.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Ulf Magnusson <ulfalizer@gmail.com>

scripts/kconfig/conf.c

@@ -39,7 +39,6 @@ static enum input_mode input_mode = oldaskconfig;
 
 static int indent = 1;
 static int tty_stdio;
-static int valid_stdin = 1;
 static int sync_kconfig;
 static int conf_cnt;
 static char line[PATH_MAX];
@@ -72,16 +71,6 @@ static void strip(char *str)
 		*p-- = 0;
 }
 
-static void check_stdin(void)
-{
-	if (!valid_stdin) {
-		printf(_("aborted!\n\n"));
-		printf(_("Console input/output is redirected. "));
-		printf(_("Run 'make oldconfig' to update configuration.\n\n"));
-		exit(1);
-	}
-}
-
 /* Helper function to facilitate fgets() by Jean Sacren. */
 static void xfgets(char *str, int size, FILE *in)
 {
@@ -113,7 +102,6 @@ static int conf_askvalue(struct symbol *sym, const char *def)
 			printf("%s\n", def);
 			return 0;
 		}
-		check_stdin();
 		/* fall through */
 	case oldaskconfig:
 		fflush(stdout);
@@ -310,7 +298,6 @@ static int conf_choice(struct menu *menu)
 				printf("%d\n", cnt);
 				break;
 			}
-			check_stdin();
 			/* fall through */
 		case oldaskconfig:
 			fflush(stdout);
@@ -645,7 +632,6 @@ int main(int ac, char **av)
 				return 1;
 			}
 		}
-		valid_stdin = tty_stdio;
 	}
 
 	switch (input_mode) {