[Android] Simplify logic for grabbing initial country-code.

The old way involved start-up code reading a value and setting a global
in template_url_prepopulate_data. Since the value can be computed
on-demand from device-information, just fetch it as needed instead.

BUG=169106
TBR=thakis

Review URL: https://codereview.chromium.org/628263004

Cr-Commit-Position: refs/heads/master@{#300317}