gdb/testsuite: remove debug output messages from testsuite

Over time I've managed to leave various debug logging messages in the
testsuite, all of which include the 'APB' tag that I use to make
searching for these easier.  None of these were required, they could
all be removed.

I have left the logging output in gdb.base/stap-probe.exp (but with
the 'APB' removed) as it looked slightly useful, and it's harmless to
keep it.  But all of the other logging lines I just removed.

There should be no change in what is tested after this commit.