cm: build: kernel: Remove obsolete checks

 * BOARD_USES_UBOOT is unused.
 * Same goes for BOARD_USES_UNCOMPRESSED_BOOT. Furthermore,
   it is superseded by TARGET_USES_UNCOMPRESSED_KERNEL.

Change-Id: I9f0e2848fcd0cd212bccacf14df55ad03f821051
1 file changed