Remove rootDir from the markdown ext's tsconfig

This was causing the output's folder structure to be based on the root of the
vscode project. This bring it in line with the other bundled extensions.

Fixes #15184

extensions/markdown/tsconfig.json

@@ -2,10 +2,9 @@
 	"compilerOptions": {
 		"module": "commonjs",
 		"target": "es5",
-		"outDir": "out",
+		"outDir": "./out",
 		"noLib": true,
-		"sourceMap": true,
-		"rootDir": "."
+		"sourceMap": true
 	},
 	"exclude": [
 		"node_modules"