Don't delete file in case of ResetFile schema mode

[jedelbo]

What, How & Why?

Fixes #7140

☑️ ToDos

• 📝 Changelog update
• 🚦 Tests (or not relevant)
• C-API, if public C++ API changed
• bindgen/spec.yml, if public C++ API changed

[coveralls-official]

Pull Request Test Coverage Report for Build jorgen.edelbo_74

• 30 of 30 (100.0%) changed or added relevant lines in 1 file are covered.
• 103 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.02%) to 91.843%

---

Files with Coverage Reduction	New Missed Lines	%
src/realm/array_string.cpp	2	88.0%
src/realm/sync/network/http.hpp	2	82.41%
src/realm/sync/network/websocket.cpp	2	74.44%
src/realm/sync/client.cpp	3	91.1%
src/realm/util/file.cpp	3	81.06%
test/test_thread.cpp	3	66.67%
src/realm/sync/noinst/client_impl_base.cpp	5	85.46%
src/realm/util/serializer.cpp	5	90.03%
src/realm/sync/transform.cpp	6	62.67%
src/realm/bplustree.cpp	7	75.72%

Totals
Change from base Build 2021:	-0.02%
Covered Lines:	235289
Relevant Lines:	256185

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💛 - Coveralls

[tgoyne]

UnsupportedFileFormatVersion is thrown when we can't upgrade the file, and I think deleting the file is clearly correct for the ResetFile schema mode then.

Deleting rather than upgrading the file was implemented due to realm/realm-swift#4470. The idea is that using ResetFile clearly only makes sense if your data is disposable and performing a slow upgrade doesn't make sense if you can just regenerate it anyway.

[jedelbo]

OK - dropping this approach