kselftest/arm64: Remove validation of extra_context from TODO

When fixing up support for extra_context in the signal handling tests I
didn't notice that there is a TODO file in the directory which lists this
as a thing to be done. Since it's been done remove it from the list.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221027110324.33802-1-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

kselftest/arm64: signal: Add a TODO list for signal handling tests

Note down a few gaps in our coverage.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210819134245.13935-7-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>