Throw error on legacy walkthrough (microsoft#155104)

Remove old walkthrough format

Author: lramos15

src/vs/workbench/contrib/welcomeGettingStarted/browser/gettingStartedService.ts

@@ -364,28 +364,14 @@ export class WalkthroughsService extends Disposable implements IWalkthroughsServ
 					};
 				}
 
-				// Legacy media config (only in use by remote-wsl at the moment)
+				// Throw error for unknown walkthrough format
 				else {
-					const legacyMedia = step.media as unknown as { path: string; altText: string };
-					if (typeof legacyMedia.path === 'string' && legacyMedia.path.endsWith('.md')) {
-						media = {
-							type: 'markdown',
-							path: convertExtensionPathToFileURI(legacyMedia.path),
-							base: convertExtensionPathToFileURI(dirname(legacyMedia.path)),
-							root: FileAccess.asFileUri(extension.extensionLocation),
-						};
-					}
-					else {
-						const altText = legacyMedia.altText;
-						if (altText === undefined) {
-							console.error('Walkthrough item:', fullyQualifiedID, 'is missing altText for its media element.');
-						}
-						media = { type: 'image', altText, path: convertExtensionRelativePathsToBrowserURIs(legacyMedia.path) };
-					}
+					throw new Error('Unknown walkthrough format detected for ' + fullyQualifiedID);
 				}
 
 				return ({
-					description, media,
+					description,
+					media,
 					completionEvents: step.completionEvents?.filter(x => typeof x === 'string') ?? [],
 					id: fullyQualifiedID,
 					title: step.title,