[SettingsProvider] fix configs cache update

The bug is that after remove(), size() changed during for loop, leaving
some obsolete keys in the cache.

BUG: 276881870
Test: atest android.deviceconfig.cts.DeviceConfigApiTests
Change-Id: I9aa5152caa454c4923429168469ae3a13b05b9ae

core/java/android/provider/Settings.java

@@ -3431,7 +3431,7 @@ public final class Settings {
                                     + " type:" + mUri.getPath()
                                     + " in package:" + cr.getPackageName());
                         }
-                        for (int i = 0; i < mValues.size(); ++i) {
+                        for (int i = mValues.size() - 1; i >= 0; i--) {
                             String key = mValues.keyAt(i);
                             if (key.startsWith(prefix)) {
                                 mValues.remove(key);