Remove problematic characters from modus-themes.org (bug#52126)

Remove problematic characters from modus-themes.org (bug#52126)

* doc/misc/modus-themes.org
(Enable and load, Font configurations for Org and others)
(Note on highlight-parentheses.el, Note on god-mode.el): Update links to
headings so that they no longer include the removed portions of text.

(Option for color-coding success state, Option for line highlighting)
(Option for line numbers, Option for parenthesis matching)
(Advanced customization, Per-theme customization settings)
(Case-by-case face specs using the themes' palette)
(Face specs at scale using the themes' palette)
(Remap face with local value, Cycle through arbitrary colors)
(Override colors, Override color saturation)
(Font configurations for Org and others, Configure bold and italic faces)
(Custom Org user faces, Update Org block delimiter fontification)
(Measure color contrast, Load theme depending on time of day)
(Backdrop for pdf-tools)
(A theme-agnostic hook for theme loading, Note on EWW and Elfeed fonts)
(Frequently Asked Questions): Remove parentheses from headings as they
can cause problems in the .texi version of the file.