Fix the issue with commands not available in the command pallette

Ensure that commands for dirty diff navigation are always available.
This is consistent with behavior in VS Code, and also with other
similar commands (such as `Next Problem/Previous Problem`) in Theia.

packages/scm/src/browser/scm-contribution.ts

@@ -194,24 +194,19 @@ export class ScmContribution extends AbstractViewContribution<ScmWidget> impleme
             isEnabled: () => !!this.scmFocus.get() && !!this.acceptInputCommand()
         });
         commandRegistry.registerCommand(SCM_COMMANDS.GOTO_NEXT_CHANGE, {
-            execute: () => this.dirtyDiffNavigator.gotoNextChange(),
-            isEnabled: () => this.dirtyDiffNavigator.canNavigate()
+            execute: () => this.dirtyDiffNavigator.gotoNextChange()
         });
         commandRegistry.registerCommand(SCM_COMMANDS.GOTO_PREVIOUS_CHANGE, {
-            execute: () => this.dirtyDiffNavigator.gotoPreviousChange(),
-            isEnabled: () => this.dirtyDiffNavigator.canNavigate()
+            execute: () => this.dirtyDiffNavigator.gotoPreviousChange()
         });
         commandRegistry.registerCommand(SCM_COMMANDS.SHOW_NEXT_CHANGE, {
-            execute: () => this.dirtyDiffNavigator.showNextChange(),
-            isEnabled: () => this.dirtyDiffNavigator.canShowChange()
+            execute: () => this.dirtyDiffNavigator.showNextChange()
         });
         commandRegistry.registerCommand(SCM_COMMANDS.SHOW_PREVIOUS_CHANGE, {
-            execute: () => this.dirtyDiffNavigator.showPreviousChange(),
-            isEnabled: () => this.dirtyDiffNavigator.canShowChange()
+            execute: () => this.dirtyDiffNavigator.showPreviousChange()
         });
         commandRegistry.registerCommand(SCM_COMMANDS.CLOSE_CHANGE_PEEK_VIEW, {
-            execute: () => this.dirtyDiffNavigator.closeChangePeekView(),
-            isEnabled: () => this.dirtyDiffNavigator.isShowingChange()
+            execute: () => this.dirtyDiffNavigator.closeChangePeekView()
         });
     }