arch/x86/irq: Purge useless handler declarations from hw_irq.h

arch/x86/include/asm/hw_irq.h contains declarations for the C-level handlers
called into directly from the IDT-referenced assembly stubs. These
declarations are never used as they are referenced from assembly only.

Furthermore, these declarations got their attributes wrong: there is no
'__irqentry' (parameter passing via stack) attached to them.

Also, the list of declarations isn't complete: none of the tracing-capable
variants is declared, for example.

Purge the handler declarations.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>