Remove unused "Developer" fixtures from tests

The `RecursiveCallbackDeveloper` and `ImmutableMethodDeveloper` classes
are not used anymore in tests, and neither is the `@cancelled` variable.
[ci skip] Fix typo
Merge pull request #17977 from yui-knk/fix/typo

[ci skip] Fix typo
Merge pull request #17972 from claudiob/remove-unused-callback-fixtures

Remove unused "Developer" fixtures from tests
Unused csv fixture file