Remove --no-use-pip-constraints option

[sbidoul]

Users should switch to a pip version that supports URL as constraints (it was only unsupported in pip 20.3 and 21.0 with the new resolver).

[codecov]

Codecov Report

Merging #60 (217d3cb) into master (00ce790) will increase coverage by 3.55%.
The diff coverage is 94.72%.

❗ Current head 217d3cb differs from pull request most recent head fc8c027. Consider uploading reports for the commit fc8c027 to get more accurate results

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
+ Coverage   92.04%   95.60%   +3.55%     
==========================================
  Files          11       16       +5     
  Lines         465      932     +467     
  Branches       86      173      +87     
==========================================
+ Hits          428      891     +463     
  Misses         27       27              
- Partials       10       14       +4     

Impacted Files	Coverage Δ
src/pip_deepfreeze/__main__.py	90.69% <77.77%> (-9.31%)	⬇️
src/pip_deepfreeze/compat.py	88.23% <88.23%> (ø)
src/pip_deepfreeze/env_info_json.py	88.88% <88.88%> (ø)
src/pip_deepfreeze/pip_list_json.py	88.88% <88.88%> (ø)
src/pip_deepfreeze/installed_dist.py	90.47% <90.47%> (ø)
src/pip_deepfreeze/sync.py	92.59% <90.90%> (+0.28%)	⬆️
src/pip_deepfreeze/tree.py	94.44% <94.44%> (ø)
src/pip_deepfreeze/pip.py	98.09% <96.96%> (+7.52%)	⬆️
src/pip_deepfreeze/list_installed_depends.py	100.00% <100.00%> (ø)
src/pip_deepfreeze/project_name.py	100.00% <100.00%> (ø)
... and 13 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 515067b...fc8c027. Read the comment docs.