Remove dead function parameters

[soininen]

Removed future=True parameters from SQLAlchemy functions which were helpful when migrating from SQLAlchemy 1.3 to 2.0 but are now effectively dead code.

No functional changes intended.

No associated issue.

Checklist before merging

• Documentation (also in Toolbox repo) is up-to-date
• Release notes have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black & isort
• Unit tests pass

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.15%. Comparing base (1e9110b) to head (f8cdf18).

Files with missing lines	Patch %	Lines
spinedb_api/db_mapping.py	75.00%	1 Missing ⚠️
spinedb_api/helpers.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #627   +/-   ##
=======================================
  Coverage   86.15%   86.15%           
=======================================
  Files          83       83           
  Lines       11477    11477           
  Branches     1636     1636           
=======================================
  Hits         9888     9888           
  Misses       1238     1238           
  Partials      351      351           

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