Remove libpac usage from Android.

Android's libpac is replaced with WebView implementation.
This will allow to remove V8 which is used only by libpac.

Bug: 165006496
Test: Manual. Remove libpac and v8 from manifest, check there are no
compilation errors.
Test: atest com.android.cts.devicepolicy.DeviceOwnerTest#testProxyPacProxyTest
Change-Id: Id6b9a223c176ce1b2dd7f7c4dd9ee54001dae1a4

Change-Id: If3ee10fcd0306b4b7a3c8b498e877d59398f642a