Remove unused headers in video_recoder plugin

[ahcorde]

Signed-off-by: ahcorde [email protected]

🦟 Bug fix

Summary

Remove unused ign-gazebo headers in video_recoder plugin.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[codecov]

Codecov Report

Merging #834 (f2da2d5) into ign-gazebo3 (0cacbd5) will increase coverage by 0.04%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           ign-gazebo3     #834      +/-   ##
===============================================
+ Coverage        77.81%   77.86%   +0.04%     
===============================================
  Files              216      216              
  Lines            12150    12150              
===============================================
+ Hits              9454     9460       +6     
+ Misses            2696     2690       -6     

Impacted Files	Coverage Δ
src/SimulationRunner.cc	94.42% <0.00%> (+1.07%)	⬆️

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