Doc: we no longer provide a list of common mnemonics

Remove the claim from the QKeySequence documentation, fixing the
respective qdoc warning.

Amends f10ae4b887.

Pick-to: 6.5
Change-Id: If234cfb0a6b7dc20fb10e623cc3ee2ec167f22c9
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/gui/kernel/qkeysequence.cpp

@@ -931,11 +931,6 @@ bool QKeySequence::isEmpty() const
     For example, mnemonic("E&xit") returns \c{Qt::ALT+Qt::Key_X},
     mnemonic("&Quit") returns \c{ALT+Key_Q}, and mnemonic("Quit")
     returns an empty QKeySequence.
-
-    We provide a \l{accelerators.html}{list of common mnemonics}
-    in English. At the time of writing, Microsoft and Open Group do
-    not appear to have issued equivalent recommendations for other
-    languages.
 */
 QKeySequence QKeySequence::mnemonic(const QString &text)
 {