arc: Remove annoying debug message

arc: Remove annoying debug message

The logging message is called too often - once for each register when it's
value has to be evaluated. This floods the screen for commands like "info
register all", but doesn't give really any help at debugging GDB issues.
Between increasing the debug level of this message and removing it altogether I
think that removing it is preferable.

gdb/ChangeLog:

	arc-tdep.c (arc_frame_prev_register): Remove annoying log message.