Remove raw new/delete calls from #205

[mjcarroll]

I think that we should generally avoid raw new and delete calls in code going forward. In this case, the test was also allocating memory without deallocating.

I replaced heap allocations with std::vector<T> where it made sense.

[codecov]

Codecov Report

Merging #206 (260c42c) into convert_rgb (fe9fffe) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           convert_rgb     #206      +/-   ##
===============================================
- Coverage        75.21%   75.20%   -0.02%     
===============================================
  Files               73       73              
  Lines            10309    10307       -2     
===============================================
- Hits              7754     7751       -3     
- Misses            2555     2556       +1     

Impacted Files	Coverage Δ
graphics/include/ignition/common/Image.hh	97.05% <100.00%> (-0.17%)	⬇️
graphics/src/SkeletonAnimation.cc	42.46% <0.00%> (-1.37%)	⬇️

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[iche033]

looks good to me, thanks!