Revert "Support a prebuilt WebView."

To work around framework resource IDs not being constant, go back to
building webviewchromium.jar from source.

This reverts commit 9c9341f1d2368b4209fe982f3f1c5de384f67fb7.

Bug: 11426593
Merge tag 'android-4.4_r1.2' into cm-11.0

Android 4.4 Release 1.2