fix: clean up the discriminator mapping in the remove-x-internal decorator

[tatomyr]

What/Why/How?

Fixed the remove-x-internal decorator, which was not removing the reference in the corresponding discriminator mapping while removing the original $ref.

Reference

Fixes https://github.com/Redocly/redocly-cli/issues/1649

Testing

Screenshots (optional)

Check yourself

• [ ] Code changed? - Tested with redoc/reference-docs/workflows (internal)
• [x] All new/updated code is covered with tests
• [ ] New package installed? - Tested in different environments (browser/node)

Security

• [x] Security impact of change has been considered
• [x] Code follows company security practices and guidelines

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: ec94fa8fca33a4a0abf5a21292552f4632ff4a95

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@redocly/openapi-core	Patch
@redocly/cli	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions[bot]]

Command	Mean [s]	Min [s]	Max [s]	Relative
redocly lint packages/core/src/benchmark/benches/rebilly.yaml	1.003 ± 0.021	0.980	1.037	1.00
redocly-next lint packages/core/src/benchmark/benches/rebilly.yaml	1.013 ± 0.015	0.989	1.046	1.01 ± 0.03

[github-actions[bot]]

Coverage report

St.:grey_question:	Category	Percentage	Covered / Total
🟡	Statements	78.81%	5011/6358
🟡	Branches	67.52%	2075/3073
🟡	Functions	73.3%	829/1131
🟡	Lines	79.12%	4729/5977

Test suite run success

811 tests passing in 121 suites.

Report generated by 🧪jest coverage report action from ec94fa8fca33a4a0abf5a21292552f4632ff4a95