Remove duplicate h.264 codec parameters from defaults

[esonderegger]

It appears as though these two sets of lines are identical:

• https://github.com/pion/webrtc/blob/master/mediaengine.go#L137-L144
• https://github.com/pion/webrtc/blob/master/mediaengine.go#L164-L171

This PR removes the second set. Question: does order matter here? If so, in which order should the h.264 codec parameters be registered with the media engine?

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.16% ⚠️

Comparison is base (ebd6753) 77.78% compared to head (96a9888) 77.63%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2465      +/-   ##
==========================================
- Coverage   77.78%   77.63%   -0.16%     
==========================================
  Files          87       87              
  Lines        9374     9378       +4     
==========================================
- Hits         7292     7281      -11     
- Misses       1653     1666      +13     
- Partials      429      431       +2     

Flag	Coverage Δ
go	79.40% <100.00%> (-0.17%)	⬇️
wasm	70.23% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
mediaengine.go	92.02% <100.00%> (+0.06%)	⬆️

... and 2 files with indirect coverage changes

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