Simplify some DefaultMediaSourceFactory instantiation in the dev guide

In many cases we're passing a 'custom' DataSource.Factory where it's not
relevant for the respective dev guide section.

#minor-release

PiperOrigin-RevId: 450374171

docs/ad-insertion.md

@@ -220,7 +220,7 @@ server-side ad insertion `MediaSource` for URIs using the `ssai://` scheme:
 Player player =
     new ExoPlayer.Builder(context)
         .setMediaSourceFactory(
-            new DefaultMediaSourceFactory(dataSourceFactory)
+            new DefaultMediaSourceFactory(context)
                 .setServerSideAdInsertionMediaSourceFactory(ssaiFactory))
         .build();
 ```
@@ -241,7 +241,7 @@ In order to use this class, you need to set up the
 ```
 // MediaSource.Factory to load the actual media stream.
 DefaultMediaSourceFactory defaultMediaSourceFactory =
-    new DefaultMediaSourceFactory(dataSourceFactory);
+    new DefaultMediaSourceFactory(context);
 // AdsLoader that can be reused for multiple playbacks.
 ImaServerSideAdInsertionMediaSource.AdsLoader adsLoader =
     new ImaServerSideAdInsertionMediaSource.AdsLoader.Builder(context, adViewProvider)

docs/drm.md

@@ -94,7 +94,7 @@ DrmSessionManager customDrmSessionManager =
     new CustomDrmSessionManager(/* ... */);
 // Pass a drm session manager provider to the media source factory.
 MediaSource.Factory mediaSourceFactory =
-    new DefaultMediaSourceFactory(dataSourceFactory)
+    new DefaultMediaSourceFactory(context)
         .setDrmSessionManagerProvider(mediaItem -> customDrmSessionManager);
 ~~~
 {: .language-java}