x86/entry: Remove the apic/BUILD interrupt leftovers

Remove all the code which was there to emit the system vector stubs. All
users are gone.

Move the now unused GET_CR2_INTO macro muck to head_64.S where the last
user is. Fixup the eye hurting comment there while at it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202119.927433002@linutronix.de

arch/x86/kernel/head_64.S

@@ -29,15 +29,16 @@
 #ifdef CONFIG_PARAVIRT_XXL
 #include <asm/asm-offsets.h>
 #include <asm/paravirt.h>
+#define GET_CR2_INTO(reg) GET_CR2_INTO_AX ; _ASM_MOV %_ASM_AX, reg
 #else
 #define INTERRUPT_RETURN iretq
+#define GET_CR2_INTO(reg) _ASM_MOV %cr2, reg
 #endif
 
-/* we are not able to switch in one step to the final KERNEL ADDRESS SPACE
+/*
+ * We are not able to switch in one step to the final KERNEL ADDRESS SPACE
  * because we need identity-mapped pages.
- *
  */
-
 #define l4_index(x)	(((x) >> 39) & 511)
 #define pud_index(x)	(((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))