Drop support for GTH board

The board maintainer states:

    The GTH board is obsolete and has not been manufactured for
    several years.
    To my knowledge, no recent U-Boot build has been tested on that
    card.

So drop support for this board.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Thomas Lange <thomas@corelatus.se>
Acked-by: Thomas Lange<thomas@corelatus.se>
diff --git a/common/env_common.c b/common/env_common.c
index 82e4936..460309b 100644
--- a/common/env_common.c
+++ b/common/env_common.c
@@ -227,7 +227,7 @@
 #endif
 
 	if (gd->env_valid == 0) {
-#if defined(CONFIG_GTH)	|| defined(CONFIG_ENV_IS_NOWHERE)	/* Environment not changable */
+#if defined(CONFIG_ENV_IS_NOWHERE)	/* Environment not changable */
 		puts ("Using default environment\n\n");
 #else
 		puts ("*** Warning - bad CRC, using default environment\n\n");