Corrected type declarations in ThemeStorage

refs https://linear.app/tryghost/issue/CORE-35/refactor-route-and-redirect-settings

- Type declarations were incorrect, co changed them to something more suitable based on the implementation to reduce the error output.

core/server/services/themes/ThemeStorage.js

@@ -60,8 +60,8 @@ class ThemeStorage extends LocalFileStorage {
     /**
      * Rename a file / folder
      *
-     *
-     * @param String fileName
+     * @param {String} srcName
+     * @param {String} destName
      */
     rename(srcName, destName) {
         let src = path.join(this.getTargetDir(), srcName);
@@ -71,9 +71,10 @@ class ThemeStorage extends LocalFileStorage {
     }
 
     /**
-     * Rename a file / folder
+     * Remove a file / folder
      *
-     * @param String backupName
+     * @param {String} fileName
+     * @returns {Promise<void>}
      */
     delete(fileName) {
         return fs.remove(path.join(this.getTargetDir(), fileName));