arm64: debug: remove unused local_dbg_{enable, disable} macros

The debug enable/disable macros are not used anywhere in the kernel, so
remove them from irqflags.h

Reported-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>