Remove compilation flag "skip_frames"

It is unused since ebccb9f6cc.

meson_options.txt

@@ -4,5 +4,4 @@ option('crossbuild_windows', type: 'boolean', value: false, description: 'Build
 option('windows_noconsole', type: 'boolean', value: false, description: 'Disable console on Windows (pass -mwindows flag)')
 option('prebuilt_server', type: 'string', description: 'Path of the prebuilt server')
 option('portable', type: 'boolean', value: false, description: 'Use scrcpy-server.jar from the same directory as the scrcpy executable')
-option('skip_frames', type: 'boolean', value: true, description: 'Always display the most recent frame')
 option('hidpi_support', type: 'boolean', value: true, description: 'Enable High DPI support')