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 #1649

Testing

Screenshots (optional)

Check yourself

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

Security

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

[changeset-bot]

🦋 Changeset detected

Latest commit: b7b20da

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

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[github-actions]

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
redocly lint packages/core/src/benchmark/benches/rebilly.yaml	968.6 ± 20.0	949.7	1010.1	1.00
redocly-next lint packages/core/src/benchmark/benches/rebilly.yaml	975.5 ± 25.5	940.6	1033.0	1.01 ± 0.03

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	78.77%	4972/6312
🟡	Branches	67.55% (+1.2% 🔼)	2059/3048
🟡	Functions	73.13%	822/1124
🟡	Lines	79.08%	4691/5932

Test suite run success

803 tests passing in 121 suites.

Report generated by 🧪jest coverage report action from b7b20da