RTC: Fix memory leak when replace rtp packet in cache.

[xiaozhihong]

• fix memory leak when replace rtp packet in cache.

[codecov-commenter]

Codecov Report

Merging #2771 (0d95b85) into 4.0release (3eb8fa2) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@              Coverage Diff               @@
##           4.0release    #2771      +/-   ##
==============================================
- Coverage       60.32%   60.32%   -0.01%     
==============================================
  Files             121      121              
  Lines           50970    50972       +2     
==============================================
  Hits            30747    30747              
- Misses          20223    20225       +2     

| Impacted Files | Coverage Δ | |'

Translated to English while maintaining the markdown structure:

'| Impacted Files | Coverage Δ | |
|---|---|---|
| trunk/src/app/srs_app_rtc_source.cpp | 12.45% <0.00%> (-0.02%) | ⬇️ |

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Translated to English while maintaining the markdown structure:

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