Remove obsolete class DownstreamChromiumBrowserProvider.

ios/chrome/browser/BUILD.gn

Index: ios/chrome/browser/BUILD.gn
diff --git a/ios/chrome/browser/BUILD.gn b/ios/chrome/browser/BUILD.gn
index 4d26fdd20fcf3f0ac5b12626fdc43fd3460ae19e..b72e1fd00e0a6b79414871edbb9f92de009cea54 100644
--- a/ios/chrome/browser/BUILD.gn
+++ b/ios/chrome/browser/BUILD.gn
@@ -257,40 +257,6 @@ source_set("browser_internal") {
   ]
 }
 
-source_set("downstream_provider") {
-  sources = [
-    "downstream_chromium_browser_provider.h",
-    "downstream_chromium_browser_provider.mm",
-  ]
-  deps = [
-    ":browser",
-    "//base",
-    "//components/pref_registry",
-    "//components/prefs",
-    "//ios/chrome/browser/autofill:autofill_internal",
-    "//ios/chrome/browser/browser_state",
-    "//ios/chrome/browser/browser_state:browser_state_impl",
-    "//ios/chrome/browser/providers",
-    "//ios/chrome/browser/sync/glue",
-    "//ios/chrome/browser/sync/sessions",
-    "//ios/chrome/browser/tabs",
-    "//ios/chrome/browser/tabs:tabs_internal",
-    "//ios/chrome/browser/ui",
-    "//ios/chrome/browser/ui/webui:webui_internal",
-  ]
-}
-
-source_set("downstream_provider_factory") {
-  sources = [
-    "downstream_chromium_browser_provider_factory.mm",
-  ]
-  deps = [
-    ":downstream_provider",
-    "//base",
-    "//ios/public/provider/chrome/browser",
-  ]
-}
-
 # Clean Skeleton targets
 source_set("browser_clean_skeleton") {
   sources = [