Delete NetworkFactory from frameworks/base/core.

It is being moved to frameworks/libs/net.

Test: builds
Test: atest FrameworksNetTests
Test: atest FrameworksWifiTests
Test: atest FrameworksTelephonyTests
Bug: 138306002
Bug: 139268426
Change-Id: I4eec40bed93679a029a20d38c114b1dbc80aa12e
Merged-In: I4eec40bed93679a029a20d38c114b1dbc80aa12e