gnu: Qt: Update to 5.15.2.

gnu: Qt: Update to 5.15.2.

* gnu/packages/qt.scm (qtbase, qtsvg, qtimageformats, qtx11extras,
qtxmlpatterns, qtdeclarative, qtconnectivity, qtwebsockets, qtsensors,
qtmultimedia, qtwayland, qtserialport, qtserialbus, qtwebchannel,
qtwebglplugin, qtwebview, qtlocation, qttools, qtscript, qtquickcontrols,
qtquickcontrols2, qtgraphicaleffects, qtgamepad, qtscxml, qtpurchasing,
qtcharts, qtdatavis3d, qtnetworkauth, qtremoteobjects, qtspeech, qtwebengine):
Update to 5.15.2.
(qtbase)[source](patches): Remove obsolete patch.
(qtwayland)[source](modules, snippet): Remove.
[inputs]: Add VULKAN-HEADERS.
(qtwebengine)[source](snippet): Adjust preserved files.
[arguments]: Remove two obsolete phases.
* gnu/packages/patches/qtbase-fix-krita-deadlock.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.