arch: mips: remove ReiserFS from defconfig

ReiserFS has been deprecated for a year and a half, yet is still built
as part of a defconfig kernel.

According to commit eb103a51

 ("reiserfs: Deprecate reiserfs"), the
filesystem is slated to be removed in 2025. Remove it from the defconfig
profiles now, as part of its deprecation process.

Signed-off-by: Peter Lafreniere <peter@n8pjl.ca>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>