m68k: defconfig: Update defconfigs for v6.15-rc1

m68k: defconfig: Update defconfigs for v6.15-rc1

  - Drop CONFIG_PRIME_NUMBERS=m (auto-modular since commit
    313b38a6ecb46db4 ("lib/prime_numbers: convert self-test to KUnit")),
  - Drop CONFIG_TEST_PRINTF=m (Replaced by auto-modular
    CONFIG_PRINTF_KUNIT_TEST in commit 7a79e7daa84e2302 ("printf:
    convert self-test to KUnit")),
  - Drop CONFIG_TEST_SCANF=m (Replaced by auto-modular
    CONFIG_SCANF_KUNIT_TEST in commit 97c1f302f2bc318e ("scanf: convert
    self-test to KUnit")),
  - Drop CONFIG_TEST_BLACKHOLE_DEV=m (replaced by auto-modular
    CONFIG_BLACKHOLE_DEV_KUNIT_TEST in commit b341f6fd45abb188
    ("blackhole_dev: convert self-test to KUnit")).

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/e7d9ff0ef58efaa3e0adcb7207e6b44d948caa25.1744615371.git.geert@linux-m68k.org