sh: Kill off now bogus fixmap/page wiring documentation.

The plans for _PAGE_WIRED were detailed in a comment with the fixmap
code, but as it's now all taken care of, we no longer have any reason for
keeping it around, particularly since it's no longer accurate. Kill it
off.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/init.c

@@ -98,21 +98,6 @@ static void clear_pte_phys(unsigned long addr, pgprot_t prot)
 	local_flush_tlb_one(get_asid(), addr);
 }
 
-/*
- * As a performance optimization, other platforms preserve the fixmap mapping
- * across a context switch, we don't presently do this, but this could be done
- * in a similar fashion as to the wired TLB interface that sh64 uses (by way
- * of the memory mapped UTLB configuration) -- this unfortunately forces us to
- * give up a TLB entry for each mapping we want to preserve. While this may be
- * viable for a small number of fixmaps, it's not particularly useful for
- * everything and needs to be carefully evaluated. (ie, we may want this for
- * the vsyscall page).
- *
- * XXX: Perhaps add a _PAGE_WIRED flag or something similar that we can pass
- * in at __set_fixmap() time to determine the appropriate behavior to follow.
- *
- *					 -- PFM.
- */
 void __set_fixmap(enum fixed_addresses idx, unsigned long phys, pgprot_t prot)
 {
 	unsigned long address = __fix_to_virt(idx);