[projmgr] Remove -R, --relative-paths option from usage page

[grasci-arm]

The -R, --relative-paths option for the list packs command was introduced as test support in #1221 but should be excluded from usage/help page (hidden option).
Reported by @ReinhardKeil

[github-actions]

Test Results

    3 files     21 suites   12m 55s ⏱️
  420 tests   420 ✅ 0 💤 0 ❌
1 260 runs  1 260 ✅ 0 💤 0 ❌

Results for commit fa44be9.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.60%. Comparing base (5022423) to head (fa44be9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2186   +/-   ##
=======================================
  Coverage   66.60%   66.60%           
=======================================
  Files         181      181           
  Lines       38417    38417           
  Branches    22511    22511           
=======================================
  Hits        25586    25586           
  Misses       8080     8080           
  Partials     4751     4751           

Flag	Coverage Δ
projmgr-cov	80.77% <100.00%> (ø)

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Files with missing lines	Coverage Δ
tools/projmgr/src/ProjMgr.cpp	80.20% <100.00%> (ø)

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