Drop support for traffic management via Ingresses

[aermakov-zalando]

We've migrated to stackset-based traffic management and don't intend to migrate back. Let's just drop the unnecessary code.

[coveralls]

Pull Request Test Coverage Report for Build 1618

• 21 of 23 (91.3%) changed or added relevant lines in 4 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+3.3%) to 72.119%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/core/types.go	17	19	89.47%

Files with Coverage Reduction	New Missed Lines	%
pkg/core/types.go	3	87.43%

Totals
Change from base Build 1597:	3.3%
Covered Lines:	1521
Relevant Lines:	2109

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💛 - Coveralls

[muaazsaleem]

👍

[mikkeloscar]

FYI: I changed the version bump from v2.0 to v1.3 i.e. just bumping the minor version. I think this is the right way because while I understand that we change the API a bit, we're not doing major changes overall to StackSet which would prompt a v2 in my mind.

[mikkeloscar]

👍

[muaazsaleem]

👍