Correctly handle cameras that are not streaming

[felipecrs]

• Refs fix: Remove [old] rtmp support #776 (comment)

This partially reverts #776, but also handles the case when birdseye would not be streaming (important to remember that birdseye doesn't even have streaming enabled by default) (EDIT: this was a mistake, birdseye entity is not even added if birdseye.restream is not enabled).

The rationale is: indeed, it is possible to have cameras in Frigate without streaming capabilities (i.e. if you don't have the camera set in your go2rtc).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (85cfdd0) to head (85e5d8a).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #782   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files           17        17           
  Lines         2048      2050    +2     
=========================================
+ Hits          2048      2050    +2     

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[dermotduffy]

Thanks @felipecrs !