Make catchpoint inherit breakpoint, eliminate init_raw_breakpoint

Make catchpoint inherit breakpoint, eliminate init_raw_breakpoint

struct catchpoint's ctor currently calls init_raw_breakpoint, which is
a bit weird, as that ctor-like function takes a sal argument, but
catchpoints don't have code locations.

Instead, make struct catchpoint's ctor add the catchpoint's dummy
location using add_dummy_location.

init_raw_breakpoint uses add_location under the hood, and with a dummy
sal it would ultimately use the breakpoint's gdbarch for the
location's gdbarch, so replace the references to loc->gdbarch (which
is now NULL) in syscall_catchpoint to references to the catchpoint's
gdbarch.

struct catchpoint's ctor was the last user of init_raw_breakpoint, so
this commit eliminates the latter.

Since catchpoint locations aren't code locations, make struct
catchpoint inherit struct breakpoint instead of base_breakpoint.  This
let's us delete the tracepoint::re_set override too.

Change-Id: Ib428bf71efb09fdaf399c56e4372b0f41d9c5869