MIPS: math-emu: Remove unused handle_dsemul function declaration

handle_dsemul does not exist and it's not being used in the code at all
so remove its declaration. The deliberate DS emulation exception is
handled by the do_dsemulret C code.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10950/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>