Build x86_64 and arm64 wheels for macOS instead of universal2 wheels …

…because the x86 wheels are still encouraged anyway.

pyproject.toml

@@ -26,6 +26,5 @@ archs = ["AMD64", "x86"]
 [tool.cibuildwheel.macos]
 # https://cibuildwheel.readthedocs.io/en/stable/faq/#what-to-provide suggests to provide
 # x86_64 and one of universal2 or arm64 wheels.  x86_64 is still required by older pips,
-# so additional arm64 wheels would suffice.  However, since the library build uses a mixed
-# amd64/arm64 setup, we build universal2 wheels regardless.
-archs = ["x86_64", "universal2"]
+# so additional arm64 wheels suffice.
+archs = ["x86_64", "arm64"]