ert Remove parameter metadata

Issue Resolves #12418

Make use that all parameters are pydantic basemodel now. (Screenshot of new behavior in GUI if applicable)

[ ] PR title captures the intent of the changes, and is fitting for release notes.
[ ] Added appropriate release note label
[ ] Commit history is consistent and clean, in line with the contribution guidelines.
[ ] Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

[ ] When there are user facing changes: Updated documentation
[ ] New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
[ ] Large PR: Prepare changes in small commits for more convenient review
[ ] Bug fix: Add regression test for the bug
[ ] Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

Dec 05 '25 13:12 xjules

Codecov Report

:x: Patch coverage is 65.95745% with 16 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 90.61%. Comparing base (c612499) to head (b3233c4).

Files with missing lines	Patch %	Lines
src/ert/storage/migration/to19.py	31.81%	15 Missing :warning:
src/ert/dark_storage/endpoints/parameters.py	50.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12466      +/-   ##
==========================================
- Coverage   90.69%   90.61%   -0.09%     
==========================================
  Files         431      432       +1     
  Lines       29734    29738       +4     
==========================================
- Hits        26968    26947      -21     
- Misses       2766     2791      +25

Flag	Coverage Δ
cli-tests	`37.59% <21.27%> (-0.04%)`	:arrow_down:
gui-tests	`68.72% <44.68%> (-0.04%)`	:arrow_down:
performance-and-unit-tests	`74.13% <57.44%> (-0.07%)`	:arrow_down:
test	`38.32% <19.14%> (-0.06%)`	:arrow_down: