vcs: remove unused method from API

This method was moved into API from the GitResolveConflictsAction in 602e6fff, but was forgotten during the multiple files merge dialog rewrite in 37382e7.

In fact there is no need to update repositories after merging files: the state of the repository doesn't change, nothing gets committed, etc.
On the other hand, if merging happens during a rebase or other complex process, a commit does happen, but repositories are updated as a part of that process.

platform/vcs-api/src/com/intellij/openapi/vcs/merge/MergeProvider.java

@@ -6,8 +6,6 @@ import com.intellij.openapi.vcs.VcsProviderMarker;
 import com.intellij.openapi.vfs.VirtualFile;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.List;
-
 
 public interface MergeProvider extends VcsProviderMarker {
   @NotNull
@@ -20,12 +18,6 @@ public interface MergeProvider extends VcsProviderMarker {
 
   boolean isBinary(@NotNull VirtualFile file);
 
-  /**
-   * Called after a multiple file merge operation with the specified list of files has been completed.
-   */
-  default void mergeDone(@NotNull List<VirtualFile> files) {
-  }
-
   /**
    * Creates a merge dialog customizer used when the default "Resolve conflicts" operation is invoked.
    */

plugins/git4idea/src/git4idea/merge/GitMergeProvider.java

@@ -471,13 +471,6 @@ public class GitMergeProvider implements MergeProvider2 {
     return new MyMergeSession(files);
   }
 
-  @Override
-  public void mergeDone(@NotNull List<VirtualFile> files) {
-    for (GitRepository repository : GitUtil.getRepositoriesForFiles(myProject, files)) {
-      repository.update();
-    }
-  }
-
   @Override
   public MergeDialogCustomizer createDefaultMergeDialogCustomizer() {
     return new GitDefaultMergeDialogCustomizer(this);