Remove SHOW SCHEDULER STATUS command and migrate the
information output to `mysqladmin debug` (COM_DEBUG)

SHOW SCHEDULER STATUS was introduced in 5.1.11, provided
some debug information about event scheduler internals and
was enabled only in debug builds.


sql/event_queue.cc:
  Remove SHOW SCHEDULER STATUS. Reporting still will be
  there but through COM_DEBUG (mysqladmin debug)
sql/event_queue.h:
  dump_internal_status cannot return an error, therefore it
  should be void.
sql/event_scheduler.cc:
  Remove SHOW SCHEDULER STATUS. Reporting still will be
  there but through COM_DEBUG (mysqladmin debug)
sql/event_scheduler.h:
  dump_internal_status cannot return an error, therefore it
  should be void.
sql/events.cc:
  Change from outputting the internal data from
  the wire to the standard output. SHOW SCHEDULER STATUS was
  removed.
sql/events.h:
  dump_internal_status() cannot return an error, therefore
  it should be void
sql/lex.h:
  remove SCHEDULER as recognized word. This is part
  of removing SHOW SCHEDULER STATUS
sql/sp_head.cc:
  SQLCOM_SHOW_SCHEDULER_STATUS has been removed
sql/sql_lex.h:
  SQLCOM_SHOW_SCHEDULER_STATUS has been removed
sql/sql_parse.cc:
  SQLCOM_SHOW_SCHEDULER_STATUS has been removed
sql/sql_test.cc:
  Dump Events' internal information on COM_DEBUG
sql/sql_yacc.yy:
  SQLCOM_SHOW_SCHEDULER_STATUS has been removed