libs: window: remove custom ref() and unref()

Use gst_object_ref() and gst_object_unref() instead.
6 jobs for gobject-window in 31 minutes and 23 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #69376
gst indent

00:00:17

passed #69375
manifest

00:00:33

 
  Build
passed #69377
build fedora x86_64

00:03:11

 
  Test
passed #69378
check fedora

00:16:58

 
  Full Builds
passed #69379
build android arm64 api28

00:05:00

passed #69380
build cerbero fedora x86_64

00:10:21