Feature: Use CMAKE_OSX_DEPLOYMENT_TARGET to get -version-min set in CMakeToolchain

[SSE4]

/cc @ssrobins
closes: #9282
set CMAKE_OSX_DEPLOYMENT_TARGET to the os.version value for macOS, iOS, watchOS, tvOS
also, remove the leftover variable DEPLOYMENT_TARGET which doesn't seem to be used/needed

Changelog: Feature: Use CMAKE_OSX_DEPLOYMENT_TARGET to get -version-min set in CMakeToolchain.
Docs: omit

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[memsharded]

Please add some unittest (no need functional or integration)