Revert "pitx-imx8m: add 'core_variant' environment variable"

- There are other automatic environment variable available:
  arch=arm
  soc=imx8m
  soc_type=imx8mq
  cpu=armv8
  So, no additional 'core_variant' variable is necessary.

This reverts commit 480e495505ef9a03af3f2b509d9bf845470bac43.

board/kontron/pitx-imx8m/pitx-imx8m.c

@@ -31,7 +31,6 @@
 #include <i2c.h>
 #include <search.h>
 #include <environment.h>
-#include <linux/ctype.h>
 
 #include "pitx-imx8m.h"
 #include "../common/emb_eep.h"
@@ -531,32 +530,9 @@ static enum boot_source pitx_imx8m_boot_source(void)
 	};
 }
 
-static void get_core_variant(char *variant, int maxlen)
-{
-	u32 cpu_rev = get_cpu_rev();
-	char *p_var = variant;
-	const char *p_cpuvar = get_imx_type((cpu_rev&0x1FF000) >> 12);
-	int len = strlen(p_cpuvar);
-
-	memset(variant, 0, maxlen);
-	if (len > maxlen)
-		len = maxlen;
-
-	/* convert variant string to lowercase */
-	for (; len > 0 ; len--, p_cpuvar++) {
-		if (*p_cpuvar != ' ')
-			*p_var++ = tolower(*p_cpuvar);
-	}
-}
-
 int board_late_init(void)
 {
-	char core_variant[32];
-
-	get_core_variant(core_variant, 32);
-	env_set("core_variant", core_variant);
 	env_set_ulong("bootsource", pitx_imx8m_boot_source());
-
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	env_set("board_name", "PITX-iMX8M");
 	env_set("board_rev", "iMX8MQ");