feat(transform_conformance): drop all babel 7 specific tests

[Boshen]

@Dunqing Is this correct?

[Boshen]

• feat(transform_conformance): drop all babel 7 specific tests #2982 👈
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #2982 will not alter performance

_{Comparing 04-14-feat_transform_conformance_drop_all_babel_7_specific_tests (c7e4f25) with main (c753c9f)}

Summary

✅ 30 untouched benchmarks

[Dunqing]

I think we don't need to drop all babel 7 tests. Because babel 8 doesn't break these tests. We just need to skip all "BABEL_8_BREAKING": true tests. (That's how it's done now.)