Fix memory leak when switching providers within a playlist [Delivers #79305128 #79031288]

[Fixes #79305128 #79031288]
Ok looks like the "defaultProvider" is only used for instream and always use jwplayer.html5.VideoProvider, i dont really know what instream means (looks like is for playing ads right?), in this case maybe is not problem for always overriding the provider (if just want to support VideoProvider), and yeah this should be named something like "forceProvider" i think