Remove all "strace" calls from the testsuite.

[Joel Brobecker]

> > The reason why I am replying is because I was wondering if you could
> > also put strace in the banned_variable list in gdb.exp? That way,
> > we're certain that it won't come back unnoticed.
> 
> The below seems to work well.

Arg - when I suggested this, I thought it would be as easy as
adding strace to an already existing list. Sorry I made you do
some extra work; not intended!

FWIW, looks great.

Thank you,
-- 
Joel