AP_NavEKF3: allow origin to be set even when using GPS

not being able to set origin when using GPS is annoying.  We've adjusted the way we do positions in the EKF (local offsets) and generally (Vector3p), so even if the suer sets an origin a long way away it shouldn't hurt.

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -1392,12 +1392,10 @@ bool NavEKF3::setOriginLLH(const Location &loc)
     if (!core) {
         return false;
     }
-    if ((sources.getPosXYSource() == AP_NavEKF_Source::SourceXY::GPS) || common_origin_valid) {
-        // we don't allow setting of the EKF origin if using GPS
-        // or if the EKF origin has already been set.
-        // This is to prevent accidental setting of EKF origin with an
-        // invalid position or height or causing upsets from a shifting origin.
-        GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "EKF3 refusing set origin");
+    if (common_origin_valid) {
+        // we don't allow resetting of the EKF origin.
+        // This is to prevent causing upsets from a shifting origin.
+        GCS_SEND_TEXT(MAV_SEVERITY_WARNING, "EKF3: origin already set");
         return false;
     }
     bool ret = false;