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>
Merge pull request #6104 from wangkx/h11703

HPCC-11703 Remove code which should not be used anymore

Reviewed-By: Gordon Smith <gordon.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>