Use connectivity APIs from framework-connectivity

Instead of compiling framework-connectivity source into
frameworks-minus-apex, have the APIs loaded separately from
framework-connectivity.

Bug: 171540887
Test: device boots, has connectivity
Change-Id: I8f07ff2082c3de80821e121807e66a43a870de7b

framework/Android.bp

@@ -35,7 +35,6 @@ java_library {
         ":framework-javastream-protos",
     ],
     apex_available: [
-        "//apex_available:platform",
         "com.android.tethering",
     ],
     jarjar_rules: "jarjar-rules-proto.txt",
@@ -125,7 +124,6 @@ java_sdk_library {
         "//packages/modules/Connectivity/Tethering/tests/unit",
     ],
     apex_available: [
-        "//apex_available:platform",
         "com.android.tethering",
     ],
 }