org-manual.org: $n$-th is not math

* doc/org-manual.org (LaTeX fragments): Do not state that dash is
allowed after single "$" math delimiter and recommend "\(...\)".

Detection of "$-" as closing math delimiters has been broken since 2015
as a side effect of using punctuation class in regular expressions while
dash is considered as a word constituent.  See commits
6779f8f424 and c0369a7984.  Bring the manual in accordance to the code
instead of allowing "($-2 change)" false positives.  Users who do not
like "\(...\)" constructs may use a helper for typing it and may change
how it is displayed to minimize visual noise by fontification, see

- Eric S Fraga to emacs-orgmode. Re: Depreciating TeX-style LaTeX
  fragments. Sun, 16 Jan 2022 12:10:30 +0000.
  <https://list.orgmode.org/87k0ezdgp5.fsf@ucl.ac.uk>
- Ihor Radchenko to emacs-orgmode. Re: [PATCH] Add support for $…$ latex
  fragments followed by a dash. Thu, 27 Jan 2022 16:28:10 +0800.
  <https://list.orgmode.org/87r18t7fc5.fsf@localhost>

doc/org-manual.org

@@ -11152,14 +11152,14 @@ snippets are identified as LaTeX source code:
  =\begin= statement appears on a new line, preceded by only
   whitespace.
 
-- Text within the usual LaTeX math delimiters.  To avoid conflicts
-  with currency specifications, single =$= characters are only
-  recognized as math delimiters if the enclosed text contains at most
-  two line breaks, is directly attached to the =$= characters with no
-  whitespace in between, and if the closing =$= is followed by
-  whitespace, punctuation or a dash.  For the other delimiters, there
-  is no such restriction, so when in doubt, use =\(...\)= as inline
-  math delimiters.
+- Text within the usual LaTeX math delimiters.  Prefer =\(...\)= for
+  inline fragments.  The =$...$= alternative has some restrictions and
+  may be a source of confusion.  To avoid conflicts with currency
+  specifications, single =$= characters are only recognized as math
+  delimiters if the enclosed text contains at most two line breaks, is
+  directly attached to the =$= characters with no whitespace in
+  between, and if the closing =$= is followed by whitespace or
+  punctuation (but not a dash).
 
 #+texinfo: @noindent
 For example: