bug#56042: 28.1; Gnus FAQ mentions removed function and variable

[Jordan Wilson]

Hi all,

in the Gnus manual's FAQ (gnus-faq.texi) in the node "Question 9.2"
there's references to `gnus-compile' and
`gnus-use-correct-string-widths'. Both of these were removed years ago.

Thanks,
Jordan Wilson
    Sent from Gnus v5.13, GNU Emacs 28.1 on WINDOWS-NT

In GNU Emacs 28.1 (build 2, x86_64-w64-mingw32)
 of 2022-04-21 built on AVALON
Windowing system distributor 'Microsoft Corp.', version 10.0.19044
System Description: Microsoft Windows 10 Home (v10.0.2009.19044.1766)

Configured using:
 'configure --with-modules --without-dbus --with-native-compilation
 --without-compress-install CFLAGS=-O2'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NATIVE_COMP
NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
XPM ZLIB