This patch converts the default_child_has_foo functions to
process_stratum_target methods.  This simplifies "regular"
non-inf_child process_stratum targets, since they no longer have to
override the target_ops::has_foo methods to call the default_child_foo
functions.  A couple targets need to override the new defaults
(corelow and tracefiles), but it still seems like a good tradeoff,
since those are expected to be little different (target doesn't run).

gdb/ChangeLog:
2018-11-30  Pedro Alves  <palves@redhat.com>

	* corelow.c (core_target) <has_all_memory, has_execution>: New
	overrides.
	* inf-child.c (inf_child_target::has_all_memory)
	(inf_child_target::has_memory, inf_child_target::has_stack)
	(inf_child_target::has_registers)
	(inf_child_target::has_execution): Delete.
	* inf-child.h (inf_child_target) <has_all_memory, has_memory,
	has_stack, has_registers, has_execution>: Delete.
	* process-stratum-target.c
	(process_stratum_target::has_all_memory)
	(process_stratum_target::has_memory)
	(process_stratum_target::has_stack)
	(process_stratum_target::has_registers)
	(process_stratum_target::has_execution): New.
	* process-stratum-target.h (process_stratum_target)
	<has_all_memory, has_memory, has_stack, has_registers,
	has_execution>: New method overrides.
	* ravenscar-thread.c (ravenscar_thread_target) <has_all_memory,
	has_memory, has_stack, has_registers, has_execution>: Delete.
	* remote-sim.c (gdbsim_target) <has_stack, has_registers,
	has_execution>: Delete.
	* remote.c (remote_target) <has_all_memory, has_memory, has_stack,
	has_registers, has_execution>: Delete.
	* target.c (default_child_has_all_memory)
	(default_child_has_memory, default_child_has_stack)
	(default_child_has_registers, default_child_has_execution):
	Delete.
	* target.h (default_child_has_all_memory)
	(default_child_has_memory, default_child_has_stack)
	(default_child_has_registers, default_child_has_execution):
	Delete.
	* tracefile.h (tracefile_target) <has_execution>: New override.