Relocate VpnManagerServiceTest and VpnTest to the frameworks

Move the files VpnManagerServiceTest and VpnTest from their
current location. Unit tests should ideally reside alongside
the code they test. The original placement likely hindered
their inclusion in module testing. Additionally, SDK checks
have been removed from the tests since they are now considered
platform tests.

Test: atest FrameworksVpnTests
Change-Id: I27b399d37c3536f4dbf39d2f8ef5242eb4ab6ba7