Deprecating secure setting install_non_market_apps

Apps targetting Android O or higher should use the new api
canRequestPackageInstalls in package manager. The secure setting
INSTALL_NON_MARKET_APPS which was used is set to 1 to make the
change transparent to apps who are already querying for this setting's
value.

Test: adb shell am instrument -e class\
'com.android.providers.settings.InstallNonMarketAppsDeprecationTest' -w\
'com.android.providers.setting.test/android.support.test.runner.AndroidJUnitRunner'

Bug: 33947615

Change-Id: Ie38d130bfccd022483a566270fce071acbdb00b7