arm64: signal: Remove unused macro

Commit 33f08261 ("arm64: signal: Allow expansion of the signal
frame") introduced the BASE_SIGFRAME_SIZE macro but it has
apparently never been used; just remove it.

Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Link: https://lore.kernel.org/r/20241029144539.111155-4-kevin.brodsky@arm.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>