ws-auth: restore zone cache cleanup in apiServerZoneDetailDELETE

[zeha]

Short description

This was lost / incorrectly replaced in #13153.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 7226124695

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 18 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.02%) to 57.724%

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Files with Coverage Reduction	New Missed Lines	%
ext/luawrapper/include/LuaContext.hpp	1	13.82%
modules/godbcbackend/sodbc.cc	2	70.8%
pdns/recursordist/test-syncres_cc1.cc	7	88.99%
pdns/packethandler.cc	8	72.84%

Totals
Change from base Build 7222412548:	0.02%
Covered Lines:	107605
Relevant Lines:	155126

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💛 - Coveralls