parisc: remove unused compat_rt_sigframe.h header

Nothing uses compat_rt_sigframe.h anymore. Commit
f671c45d

 ("[PARISC] Arch-specific compat
signals") removed all includes of that header. It also basically copied
that entire header verbatim into signal32.h. It seems it was just
forgotten to also remove compat_rt_sigframe.h from the tree. Remove that
header now.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Helge Deller <deller@gmx.de>