uridecodebin: Drop hardcoded list of media suitable for download buffering

uridecodebin: Drop hardcoded list of media suitable for download buffering

Discussion on IRC indicated that the main reason for this list was to
prevent demuxers that can trigger a lot of seeking from using
progressive buffering using queue2 (which due to being seekable triggers
that behaviour).

However given that upstream can indicate seeks are possible but should
be avoided via a scheduling query, this extra whitelisting shouldn't be
necessary for well-behaved demuxers.

https://bugzilla.gnome.org/show_bug.cgi?id=704933