Rover: remove non-functional RST_SWITCH_CH parameter

RST_SWITCH_CH is documented as "RC channel to use to reset to last flight
mode after geofence takeover", but nothing in Rover reads it. The member it
binds to, reset_switch_chan, has exactly two references in the tree: its
declaration and its GSCALAR. There is no reset-on-geofence-takeover
behaviour in Rover for it to control.

Plane went through this already. It removed its own RST_SWITCH_CH in favour
of the MODE_SWITCH_RESET RC auxiliary function, and carries a conversion for
it in its conversion_table[]. Rover has no MODE_SWITCH_RESET handler, so
there is nothing here to convert to and no behaviour to preserve: the
parameter is simply doing nothing.

Removed in the usual way, leaving a "RST_SWITCH_CH was here" marker and
keeping the k_param_reset_switch_chan key so the enumeration after it does
not shift.

The companion RESET_SWITCH_CHAN_PWM define, the other half of the same
removed feature, goes in #34213.

This drops Rover:RST_SWITCH_CH from the generated parameter metadata and
nothing else, and saves 80 bytes of flash on SITL.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Rover/Parameters.cpp

@@ -21,11 +21,7 @@ const AP_Param::Info Rover::var_info[] = {
     // @User: Advanced
     GSCALAR(log_bitmask,            "LOG_BITMASK",      DEFAULT_LOG_BITMASK),
 
-    // @Param: RST_SWITCH_CH
-    // @DisplayName: Reset Switch Channel
-    // @Description: RC channel to use to reset to last flight mode after geofence takeover.
-    // @User: Advanced
-    GSCALAR(reset_switch_chan,      "RST_SWITCH_CH",    0),
+    // RST_SWITCH_CH was here
 
     // @Param: INITIAL_MODE
     // @DisplayName: Initial driving mode

Rover/Parameters.h

@@ -41,7 +41,7 @@ public:
         //
         k_param_log_bitmask_old = 10,  // unused
         k_param_num_resets_old,         // unused
-        k_param_reset_switch_chan,
+        k_param_reset_switch_chan,  // unused
         k_param_initial_mode,
         k_param_scheduler,
         k_param_relay,
@@ -237,7 +237,6 @@ public:
     // Misc
     //
     AP_Int32    log_bitmask;
-    AP_Int8     reset_switch_chan;
     AP_Int8     initial_mode;
 
     // navigation parameters