block: remove upload from block_prepare()
block: remove upload from block_prepare()

There is no reason to keep this upload because buffer_last_upload_time
is set to -1 in the init function, so the first call to
ngli_node_block_upload() will perform the upload.

gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl