doc: simplify format description of urlObject.auth

The "at sign" is properly the "commercial at" but let's just avoid the
whole naming issue by putting the symbol right in the sentence.

PR-URL: nodejs#22324
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Bryan English <bryan@bryanenglish.com>

doc/api/url.md

@@ -920,9 +920,9 @@ The legacy `urlObject` (`require('url').Url`) is created and returned by the
 
 The `auth` property is the username and password portion of the URL, also
 referred to as _userinfo_. This string subset follows the `protocol` and
-double slashes (if present) and precedes the `host` component, delimited by an
-ASCII "at sign" (`@`). The string is either the username, or it is the username
-and password separated by `:`.
+double slashes (if present) and precedes the `host` component, delimited by `@`.
+The string is either the username, or it is the username and password separated
+by `:`.
 
 For example: `'user:pass'`.