Revert "Guess terminal background even if stdout is not a tty"

This reverts commit 887cd83ebe.

src/init.c

@@ -1008,6 +1008,11 @@ guess_terminal_background(int *r, int *g, int *b)
     *g = -1;
     *b = -1;
 
+    /* Don't guess if stdout not a terminal */
+    if (!isatty(STDOUT_FILENO)) {
+        return;
+    }
+
     ttyfd = open("/dev/tty", O_RDWR);
     if (ttyfd < 0) {
         return;