The use of the channel library as a cache for metadata to avoid
re-requesting metadata for known media is an optimization that dates
back to 1.0. However, it doesn't have any TTL, is prone to bugs, and is
of dubious value.
This commit ignores the results of the library check when queueing a new
video, opting to always re-request the metadata. This fixes a few bugs:
* Google Drive metadata being lost when storing in library
* Streamable metadata being lost when storing in library
* Videos in the channel library that are now unavailable on their
source website being queueable and then failing to play (e.g. deleted
YouTube videos).
In its place, a small fail-open check is left behind to emit metric
counters on how many queues would have been cache-hits, to provide
insight into whether a proper caching solution (i.e. one not tacked on
top of the library) would be worth pursuing or not. This will be
removed eventually.
