fix: Use removeprefix instead of lstrip or ternary operator

[effigies]

We had some .lstrip()s that should be removeprefix() as well as some pre-removeprefix() hacks of the form s[len(prefix):] if s.startswith(prefix) else s.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 48.24%. Comparing base (0218f4f) to head (5c55606).
Report is 4 commits behind head on maint/24.1.x.

Files with missing lines	Patch %	Lines
fmriprep/utils/bids.py	0.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (0218f4f) and HEAD (5c55606). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (0218f4f)	HEAD (5c55606)
	7	4

Additional details and impacted files

@@                Coverage Diff                @@
##           maint/24.1.x    #3409       +/-   ##
=================================================
- Coverage         71.78%   48.24%   -23.54%     
=================================================
  Files                57       57               
  Lines              4256     4255        -1     
  Branches            458      458               
=================================================
- Hits               3055     2053     -1002     
- Misses             1086     2133     +1047     
+ Partials            115       69       -46     

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