tests: drivers: flash: remove platform_allow filter

Prior to commit 903a7943, drivers.flash.common.default would have
executed on any platform that passed the filter condition. With the
addition of the platform_allow filter, this is no longer the case, and
is masking issues such as those seen in #62963. Remove the
platform_allow filter to return this test to the previous behavior.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>