[PATCH] Remove trad_frame_set_reg_unknown declaration

[Joel Brobecker]

> The trad_frame_set_reg_unknown declaration was added in commit
> 0db9b4b70969 (March 2004), but apparently never defined or referenced.
> 
> gdb/ChangeLog:
> 
> 	* trad-frame.h (trad_frame_set_reg_unknown): Remove declaration.

LGTM, go ahead and push.

Thank you!

-- 
Joel