arm64: pkeys: remove redundant WARN

arm64: pkeys: remove redundant WARN

FEAT_PAN3 is present if FEAT_S1POE is, this WARN() was to represent that.
However execute_only_pkey() is always called by mmap(), even on a CPU without
POE support.

Rather than making the WARN() conditional, just delete it.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: https://lore.kernel.org/linux-arm-kernel/CA+G9fYvarKEPN3u1Ogw2pcw4h6r3OMzg+5qJpYkAXRunAEF_0Q@mail.gmail.com/
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20240910105004.706981-1-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>