Fix leaks of 'per program space' and 'per inferior' ada task data.

Fix leaks of 'per program space' and 'per inferior' ada task data.

Valgrind reports leaks such as the below.
Fix these leaks by changing ada_tasks_pspace_data_handle
and ada_tasks_inferior_data_handle to use the 'with_cleanup' register variant.

Tested on debian/amd64 natively and under Valgrind.

==26346== 56 bytes in 1 blocks are definitely lost in loss record 631 of 3,249
==26346==    at 0x4C2C4CC: operator new(unsigned long) (vg_replace_malloc.c:344)
==26346==    by 0x38F911: get_ada_tasks_inferior_data(inferior*) (ada-tasks.c:281)
==26346==    by 0x38FA3F: ada_tasks_invalidate_inferior_data (ada-tasks.c:1362)
==26346==    by 0x38FA3F: ada_tasks_new_objfile_observer(objfile*) (ada-tasks.c:1411)
==26346==    by 0x60CBC5: operator() (functional:2127)
==26346==    by 0x60CBC5: notify (observable.h:106)
==26346==    by 0x60CBC5: clear_symtab_users(enum_flags<symfile_add_flag>) (symfile.c:2903)
...

==26346== 104 bytes in 1 blocks are definitely lost in loss record 984 of 3,249
==26346==    at 0x4C2E0BC: calloc (vg_replace_malloc.c:762)
==26346==    by 0x4056F0: xcalloc (common-utils.c:84)
==26346==    by 0x38F8AE: xcnew<ada_tasks_pspace_data> (poison.h:122)
==26346==    by 0x38F8AE: get_ada_tasks_pspace_data(program_space*) (ada-tasks.c:253)
==26346==    by 0x38FA77: ada_tasks_invalidate_pspace_data (ada-tasks.c:1354)
==26346==    by 0x38FA77: ada_tasks_new_objfile_observer(objfile*) (ada-tasks.c:1394)
==26346==    by 0x60CBC5: operator() (functional:2127)
==26346==    by 0x60CBC5: notify (observable.h:106)
...

gdb/ChangeLog
2019-02-18  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* ada-task.c (_initialize_tasks): Use 'with_cleanup' register
	variant for ada_tasks_pspace_data_handle and
	ada_tasks_inferior_data_handle.
	(ada_tasks_pspace_data_cleanup): New function.
	(ada_tasks_inferior_data_cleanup): New function.