refactor!: Remove deprecated methods

[Gustl22]

Description

I missed to remove the deprecated methods in #1453.

We can either:

• Add a minor version 5.1.0 for a release, as the migration instructions for the introduced breaking changes were already explained in the previous PRs.
• As it's breaking, we could release 6.0.0 instantly
• Wait with this PR and merge it until another breaking change cannot be circumvented, as this change is not urgent.

I'd propose the first or the last option.

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, refactor:,
  docs:, chore:, test:, ci: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation and added dartdoc comments with ///, where necessary.
• I have updated/added relevant examples in example.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Migration instructions

See #1352 and #1443

Related Issues

Closes #1453

[Gustl22]

@spydon any opinion on this? Thank you for reviewing ;D

[spydon]

@spydon any opinion on this? Thank you for reviewing ;D

Hmm, since we don't really have a strategy for this library yet I think you can choose whichever you think fits the best. :)