HPCC-11703 Remove code which should not be used anymore

Start/Stop/RemoteExec had been removed from System Server page.
The showPreflightControl() will fail if we try to set an element
which does not exist. Due to the failure, the function for
collapsing ftslave is not called.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>