fix: Remove Code block background highlighting

The code block highlighting code was terribly slow for large files
and is already implemented in the main app much more efficiently.

TIPS.md

@@ -155,12 +155,8 @@ div.CodeMirror .cm-overlay.cm-rm-list-token {
 
 ## Code Blocks
 
-```css
-/* Add a background color to code blocks */
-div.CodeMirror .cm-rm-code-block {
-  background-color: lightgrey;
-}
-```
+Code block highlighting is implemented by the main Joplin app as of v2.3.4 and was removed from Rich Markdown  versions 0.8.0 onwards.
+
 
 ## Colour Schemes
 

src/overlay.ts

@@ -32,18 +32,6 @@ export const blockquote_regex = /^\s*\>+\s/g;
 // TODO: Extend this to get better table highlighting
 export const table_regex = /^\|[^\n]+\|/g;
 
-// Special function to apply a line class to code blocks
-function codeBlock(cls: string) {
-	return (cm: any, line: number, state: any) => {
-		if (state?.outer && (state?.outer?.code || (state?.outer?.thisLine?.fencedCodeEnd))) {
-			cm.addLineClass(line, 'wrap', cls);
-		}
-		else {
-			cm.removeLineClass(line, 'wrap', cls);
-		}
-	}
-}
-
 function exec(query: RegExp, stream: any) {
 	query.lastIndex = stream.pos;
 	return query.exec(stream.string);
@@ -106,10 +94,6 @@ const overlays = [
 	regexOverlay('rm-hr line-cm-rm-hr', hr_regex, ['extraCSS']),
 ];
 
-const blocks = [
-	codeBlock('cm-rm-code-block')
-];
-
 function validate(settings: any, values: string[]): boolean {
 	for (let value of values) {
 		if (!settings[value])
@@ -132,15 +116,3 @@ export function remove(cm: any) {
 		cm.removeOverlay(overlay);
 }
 
-// from and to are ignored for now becuase a change on one line
-// can affect any number of other lines, this means we need to 
-// reprocess the entire document
-export function onSourceChanged(cm: any, from: number, to: number) {
-	for (let i = cm.firstLine(); i <= cm.lastLine(); i++) {
-		const state = cm.getStateAfter(i, true);
-
-		for (let block of blocks) {
-			block(cm, i, state);
-		}
-	}
-}

src/richMarkdown.ts

@@ -60,7 +60,6 @@ module.exports = {
 					ImageHandlers.clearAllWidgets(this);
 					ImageHandlers.onSourceChanged(this, this.firstLine(), this.lastLine());
 					ImageHandlers.afterSourceChanges(this);
-					Overlay.onSourceChanged(this, this.firstLine(), this.lastLine());
 					if (newSettings.activeLine) {
 						this.setOption('styleActiveLine', { nonEmpty: true });
 					} else {
@@ -102,7 +101,6 @@ module.exports = {
 					const { from, to } = get_change_lines(change);
 
 					ImageHandlers.onSourceChanged(cm, from, to);
-					Overlay.onSourceChanged(cm, from, to);
 				}
 				function on_update(cm: any) {
 					ImageHandlers.afterSourceChanges(cm);