Make the server unlink itself

To clean up the device, the client executed "adb shell rm" once the
server was guaranteed to be started (after the connection succeeded).

This implied to track whether the installation state, and failed if an
additional tunnel was used in "forward" mode:
<https://github.com/Genymobile/scrcpy/issues/386#issuecomment-453936034>

Instead, make the server unlink itself on start.

app/src/server.h

@@ -13,7 +13,6 @@ struct server {
     SDL_bool tunnel_enabled;
     SDL_bool tunnel_forward; // use "adb forward" instead of "adb reverse"
     SDL_bool send_frame_meta; // request frame PTS to be able to record properly
-    SDL_bool server_copied_to_device;
 };
 
 #define SERVER_INITIALIZER {              \
@@ -25,7 +24,6 @@ struct server {
     .tunnel_enabled = SDL_FALSE,          \
     .tunnel_forward = SDL_FALSE,          \
     .send_frame_meta = SDL_FALSE,         \
-    .server_copied_to_device = SDL_FALSE, \
 }
 
 // init default values