Revert "GCS: Fix typo for optional SDL"

This reverts commit ddbbc02aae86738edb26710687ac7dbbbf94aca4.
Revert "Merge pull request #440 from kubark42/gcs-control-via-gcsreceiver"

This reverts commit c2fba6ea63fdb17a99be6750297e384ff5f80f2e, reversing
changes made to a24176f9e7c43cf777d3b5fc65d9ca30d1b71907.

The way SDL was reenabled was broken.  Reverting this merge.