uboot-mediatek: update to U-Boot 2023.01

Support for MT7981 and MT7986 has been merged, remove patches.
Tested on a couple of MT7986, MT7622 and MT7623 boards.
MIPS builds are untested.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/boot/uboot-mediatek/patches/220-cmd-env-readmem.patch

@@ -1,6 +1,6 @@
 --- a/cmd/Kconfig
 +++ b/cmd/Kconfig
-@@ -579,6 +579,12 @@ config CMD_ENV_EXISTS
+@@ -591,6 +591,12 @@ config CMD_ENV_EXISTS
  	  Check if a variable is defined in the environment for use in
  	  shell scripting.