refactor: Cleanup report module

[gfieni]

PR overview:

• Remove the unused procfs report ;
• Remove unused methods from power and hwpc reports ;
• Cleanup the unit tests of the report module.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.98%. Comparing base (c5573c7) to head (48980d0).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #609      +/-   ##
==========================================
- Coverage   69.10%   68.98%   -0.12%     
==========================================
  Files          75       73       -2     
  Lines        2874     2757     -117     
==========================================
- Hits         1986     1902      -84     
+ Misses        888      855      -33     

Files with missing lines	Coverage Δ
src/powerapi/cli/generator.py	84.37% <100.00%> (-0.10%)	⬇️
src/powerapi/dispatch_rule/__init__.py	100.00% <ø> (ø)
src/powerapi/report/__init__.py	100.00% <100.00%> (ø)
src/powerapi/report/hwpc_report.py	92.20% <ø> (+0.95%)	⬆️
src/powerapi/report/power_report.py	81.33% <ø> (+4.86%)	⬆️
src/powerapi/report/report.py	95.08% <ø> (+1.33%)	⬆️

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