Drop support for Android HTTP stack

All future releases will use the Chromium HTTP stack and maintaining two HTTP
    stacks adds maintenance overhead. The Chromium HTTP stack requires V8, but we
    now use V8 in all build targets (b/5495373), so we can safely drop the Android
    HTTP stack.

LoadListener, HttpAuthHandlerImpl, Network, SslErrorHandlerImpl, WebViewWorker
- Android-stack specific, removed
StreamLoader, FrameLoader
- Require LoadListener, removed
CacheLoader, ContentLoader, DataLoader, FileLoader
- Extend StreamLoader, removed

BrowserFrame
- Removed methods that create LoadListener
- BrowserFrame.startLoadingResource() is called from native
CallbackProxy, WebView
- Removed calls to Network methods
CacheManager, CookieManager, CookieSyncManager, WebViewCore, WebResourceResponse
- Removed other Android-stack specific code
JniUtlil
- Removed useChromiumHttpStack()
WebViewDatabase
- Removed all code to create cookies and cache databases for Android HTTP stack

See corresponding WebKit change https://android-git.corp.google.com/g/166327.

Bug: 5495616
Change-Id: If491675516f6eb187077af4220214bb6e6a8d045