refactor: drop db migration patch (#5519)

* refactor: remove database migration patch & test

Drop migration code since it's been 6 months since 4.0.2 and we no
longer need this.

See: https://github.com/coder/code-server/issues/5482#issuecomment-1222608635

* chore: refresh patches

patches/disable-builtin-ext-update.diff

@@ -18,7 +18,7 @@ Index: code-server/lib/vscode/src/vs/workbench/contrib/extensions/browser/extens
  			if (!this.local.preRelease && this.gallery.properties.isPreReleaseVersion) {
  				return false;
  			}
-@@ -1122,6 +1126,10 @@ export class ExtensionsWorkbenchService
+@@ -1122,6 +1126,10 @@ export class ExtensionsWorkbenchService 
  				// Skip if check updates only for builtin extensions and current extension is not builtin.
  				continue;
  			}