As mentioned in #4718, this module has been rotting in the plugins package for several years and should be removed.
It was added in d499a48 back in 2014 and was used by the following plugins
$ git log --format=reference -S common_jwplayer -- src/
3c851805 (plugins.tv5monde: remove plugin, 2021-10-07)
57eea0fb (plugins.sportal: Removed old RTMP streams, use HLS, 2018-08-04)
e50e60b2 (Add support for TV5Monde, 2017-06-02)
8329f701 (plugins.sportal: added support for the live stream on sportal.bg, 2017-01-10)
777a96f9 (plugins.euronew: update to support the new site (#141), 2016-11-08)
30fb8623 (Fix connectcast.tv livestreaming, 2015-02-01)
dca69a2a (plugins.euronews: Update for service changes., 2014-09-03)
d499a488 (plugins.connectcast: Move JWPlayer playlist parsing to support plugin., 2014-09-03)
The docs's plugins extension and the generic plugins tests still have checks for modules inside the plugins package whose file name starts with common_, but those checks don't necessarily have to be removed with the removal of the (last) common_ module: