Add remote-tracking branch pruning

[seachicken]

• With --dry-run: Do not pruning
• Without --dry-run: git remote prune after removing branches

Resolves #67

[codecov[bot]]

Codecov Report

Merging #68 (4d66bb4) into main (7db7383) will decrease coverage by 1.03%. The diff coverage is 78.26%.

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
- Coverage   89.24%   88.21%   -1.04%     
==========================================
  Files           3        3              
  Lines         586      594       +8     
==========================================
+ Hits          523      524       +1     
- Misses         48       54       +6     
- Partials       15       16       +1     

Impacted Files	Coverage Δ
main.go	77.34% <42.85%> (-2.17%)	:arrow_down:
poi.go	90.74% <93.75%> (-0.64%)	:arrow_down:

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.