TST: remove wrong test testing the wrong thing

The test tried to test the effect of setting the MACOS_BUILD_TARGET
environment variable on the produced wheel tags, however there is bug
for which the emitted tags are always compared to the tag for the
current platform. The environment variable has no effect on the wheel
tags. Remove the bogus test.

tests/test_tags.py

@@ -93,18 +93,3 @@ def test_tag_mixed_abi(monkeypatch):
         'platlib': [f'extension{ABI3SUFFIX}', f'another{SUFFIX}'],
     })
     assert str(builder.tag) == f'{INTERPRETER}-{ABI}-{PLATFORM}'
-
-
-@pytest.mark.skipif(platform.system() != 'Darwin', reason='macOS specific test')
-def test_tag_macos_build_target(monkeypatch):
-    monkeypatch.setenv('MACOS_BUILD_TARGET', '12.0')
-    builder = wheel_builder_test_factory(monkeypatch, {
-        'platlib': [f'extension{SUFFIX}'],
-    })
-    assert builder.tag.platform == re.sub(r'\d+\.\d+', '12.0', PLATFORM)
-
-    monkeypatch.setenv('MACOS_BUILD_TARGET', '10.9')
-    builder = wheel_builder_test_factory(monkeypatch, {
-        'platlib': [f'extension{SUFFIX}'],
-    })
-    assert builder.tag.platform == re.sub(r'\d+\.\d+', '10.9', PLATFORM)