Allocate breakpoint_objfile_data with new

Allocate breakpoint_objfile_data with new

Allocate with new and free with delete.  This allows using an
std::vector in the following patch.

I renamed free_breakpoint_probes to free_breakpoint_objfile_data,
because it now doesn't only free the probes vector, but also the
breakpoint_objfile_data structure itself.

gdb/ChangeLog:

	* breakpoint.c (breakpoint_objfile_data): Initialize fields.
	(get_breakpoint_objfile_data): Allocate breakpoint_objfile_data
	with new.
	(free_breakpoint_probes): Rename to ...
	(free_breakpoint_objfile_data): ... this, and call delete on
	bp_objfile_data..