rtmp: simplify API

[aler9]

No description provided.

[codecov]

Codecov Report

Merging #2130 (2b40ad1) into main (72b1d23) will decrease coverage by 0.04%.
Report is 1 commits behind head on main.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main    #2130      +/-   ##
==========================================
- Coverage   62.32%   62.29%   -0.04%     
==========================================
  Files         104      104              
  Lines       11342    11372      +30     
==========================================
+ Hits         7069     7084      +15     
- Misses       3770     3782      +12     
- Partials      503      506       +3     

Files Changed	Coverage Δ
internal/rtmp/conn.go	63.54% <81.25%> (+0.44%)	⬆️
internal/core/rtmp_conn.go	61.29% <100.00%> (+0.73%)	⬆️
internal/core/rtmp_source.go	70.80% <100.00%> (-0.43%)	⬇️

... and 2 files with indirect coverage changes

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