WebView: remove unused DATA_REDUCTION_PROXY_SETTING_CHANGED API

This API was unused. We're removing this under recommendation from the
API council.

This is a manual change to prebuilts/sdk to accompany ag/2677974

Bug: 62425491
Test: make -j40
Change-Id: I7a29d306286fc8b7aaba479ee1de3955f5d4eef9
1 file changed