Update docs after modularization of docs

The global files now live in qtbase only, and are made available to the
other modules via the $QT_INSTALL_DOCS variable.

Change-Id: I131408e27fec5b722ac1dece8e1ccf421fdaad67
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>