qdoc: Eliminate uses of qmlModuleIdentifier()

The QML module identifier is no longer useful.
The function to generate it is retained for now.

Task-number: QTBUG-32173
Change-Id: Ic811ed432f2059c0370e9e0d86b2e334b5c82a3c
Reviewed-by: Martin Smith <martin.smith@digia.com>
qdoc: Remove algorithm to find common prefix

HtmlGenerator::generateCompactList() no longer uses an algorithm to
find out a common prefix for classes/qml types when generating the
alphabetical lists. The common prefix argument is no longer optional.
To indicate there is no common prefix, pass an empty string as the
common prefix argument.

Task-number: QTBUG-33750
Change-Id: I4b44bbcff909fcea5c7bfd58c6796e303086bc68
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Doc: Remove unused variable in QThread snippet

Task-number: QTBUG-33120

Change-Id: Icfc896f0b3cd78ba681e587d78c9e46f8ca89694
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>