[DarkMode] remove enableLegacyPatching option

The option was only allowed to be set to `false`, so it's not been
used at all, so now we can remove it, given that we've had the dark
mode legacy patching disabled without any major bugs in the past few
weeks.

Bug: chromium:1152736
Change-Id: I1e794d75f9c354a0d16b1b3975f7ebdf82b3448b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2988303
Commit-Queue: Jack Franklin <[email protected]>
Reviewed-by: Paul Lewis <[email protected]>
diff --git a/front_end/panels/elements/ClassesPaneWidget.ts b/front_end/panels/elements/ClassesPaneWidget.ts
index f3a3a78..9bc84f0 100644
--- a/front_end/panels/elements/ClassesPaneWidget.ts
+++ b/front_end/panels/elements/ClassesPaneWidget.ts
@@ -47,7 +47,7 @@
 
   constructor() {
     super(true);
-    this.registerRequiredCSS('panels/elements/classesPaneWidget.css', {enableLegacyPatching: false});
+    this.registerRequiredCSS('panels/elements/classesPaneWidget.css');
     this.contentElement.className = 'styles-element-classes-pane';
     const container = this.contentElement.createChild('div', 'title-container');
     this._input = container.createChild('div', 'new-class-input monospace');