Remove some cases of unnecessary std::move on return

[benjaminwinger]

These are all doing moves on temporary values wrapped in unique_ptr and the move is unnecessary and produces a compiler warning.

One's not actually when returning, but is a move on an in-place constructed value where it's already an rvalue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9147b85) 92.91% compared to head (0006eb7) 92.90%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2555      +/-   ##
==========================================
- Coverage   92.91%   92.90%   -0.02%     
==========================================
  Files        1025     1025              
  Lines       38401    38401              
==========================================
- Hits        35679    35675       -4     
- Misses       2722     2726       +4     

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