Replace gst_buffer_(make|is)_metadata_writable patch now that the release is out.

Replace gst_buffer_(make|is)_metadata_writable patch now that the release is out.

Original commit message from CVS:
* gst/gstbuffer.c: (gst_buffer_is_metadata_writable),
(gst_buffer_make_metadata_writable):
* gst/gstbuffer.h:
* libs/gst/base/gstbasetransform.c:
(gst_base_transform_prepare_output_buf):
* plugins/elements/gstcapsfilter.c: (gst_capsfilter_prepare_buf):
* tests/check/gst/gstbuffer.c: (GST_START_TEST), (gst_test_suite):
Replace gst_buffer_(make|is)_metadata_writable patch now
that the release is out.