Use removeprefix and removesuffix string methods

[johannaengland]

Dependent on #2901.

These methods have been added to Python 3.9: https://peps.python.org/pep-0616/

They remove the prefix/suffix if it exists and do nothing to the string if not.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 60.19%. Comparing base (35f1a9b) to head (93088aa).
Report is 6 commits behind head on master.

Files	Patch %	Lines
python/nav/web/geomap/db.py	0.00%	2 Missing ⚠️
python/nav/bin/navmain.py	0.00%	1 Missing ⚠️
python/nav/ipdevpoll/plugins/dot1q.py	0.00%	1 Missing ⚠️
python/nav/statemon/checker/FtpChecker.py	0.00%	1 Missing ⚠️
python/nav/statemon/checker/MysqlChecker.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2911      +/-   ##
==========================================
- Coverage   60.20%   60.19%   -0.02%     
==========================================
  Files         601      601              
  Lines       43981    43969      -12     
==========================================
- Hits        26480    26468      -12     
  Misses      17501    17501              

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[github-actions]

Test results

       9 files         9 suites   7m 46s ⏱️
3 320 tests 3 320 ✔️ 0 💤 0 ❌
6 379 runs  6 379 ✔️ 0 💤 0 ❌

Results for commit 93088aa.