purge all references to ICON_URL_LARGE, its unused

This was only partially hooked up and often not even populated.
It was added in 4895e2d790, but things have
changed a lot now.  We should be moving towards preferring the drawable XML
vector icons, which will scale nicely for all DPIs.

app/src/test/java/org/fdroid/fdroid/updater/IndexV1UpdaterTest.java

@@ -271,7 +271,6 @@ public class IndexV1UpdaterTest extends FDroidProviderTest {
                 "flattrID",
                 "icon",
                 "iconUrl",
-                "iconUrlLarge",
                 "issueTracker",
                 "lastUpdated",
                 "liberapayID",