Remove x-position from setactivityposition

After discussing with Ally and Dav, we came to the agreement that this
is basically useless since the prompt will always be centered and take
up most of the horizontal space of the screen.

And the x-position was only added as an offset because at some point,
there was a missing space from the side of the "- Press ENTER to
Teleport -" prompt, and the offset was there so people could mimic the
prompt accordingly. But that was fixed at some point, so it's useless
now.

desktop_version/src/Game.h

@@ -430,7 +430,7 @@ public:
     bool activetele;
     int readytotele;
     int oldreadytotele;
-    int activity_r, activity_g, activity_b, activity_x, activity_y;
+    int activity_r, activity_g, activity_b, activity_y;
     std::string activity_lastprompt;
     uint32_t activity_print_flags;