sparc32: remove deadwood swift_flush_tlb_page() debug code

sparc32: remove deadwood swift_flush_tlb_page() debug code

Remove an #if 0 block that has been dead since at least
Linux 2.6.12.  The block was marked "P3: deadwood to debug
precise flushes on Swift" and contained a never-compiled
alternative implementation of swift_flush_tlb_page().  It also
referenced the since-removed srmmu_flush_tlb_page(), dropped
in commit 3d5f7d37c8b4 ("sparc32: drop unused functions in
pgtsrmmu.h").

Assisted-by: unnamed:deepseek-v3.2 coccinelle
Signed-off-by: Kexin Sun <kexinsun@smail.nju.edu.cn>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Andreas Larsson <andreas@gaisler.com>