RFC: remove gdbarch from struct breakpoint

[Joel Brobecker]

> This patch removes the 'gdbarch' field from struct breakpoint.
> 
> In most cases, it is sufficient to replace the use of this field with
> the location's gdbarch instead.  In fact, I think the cases in
> tracepoint.c where this is not done are probably latent bugs.

I think that makes sense. I am trying to figure out how a breakpoint
could have a gdbarch that made some sort of sense when the breakpoint
has two locations and each location had a different gdbarch from
the other....

-- 
Joel