media: Convert mojo media defines to buildflags

content/browser/BUILD.gn

Index: content/browser/BUILD.gn
diff --git a/content/browser/BUILD.gn b/content/browser/BUILD.gn
index f87748465db77dbba99ab07aeac921bde7a1a66f..705f5f5df426a8542f8955fe546b3917d5332182 100644
--- a/content/browser/BUILD.gn
+++ b/content/browser/BUILD.gn
@@ -93,6 +93,7 @@ source_set("browser") {
     "//media/gpu/ipc/client",
     "//media/midi",
     "//media/midi:mojo",
+    "//media/mojo:features",
     "//media/mojo/interfaces",
     "//media/mojo/services",
     "//mojo/common",
@@ -2114,10 +2115,6 @@ source_set("browser") {
     deps += [ "//third_party/boringssl" ]
   }
 
-  if (enable_mojo_media) {
-    configs += [ "//media/mojo/services:mojo_media_config" ]
-  }
-
   if (use_ozone) {
     deps += [ "//ui/ozone" ]
   }