cmake: Don't try to install empty sounds directory

As git doesn't know about directories, we can't keep the empty sounds
directory in git, so remove the install command for it as well.

Fixes #118

CMakeLists.txt

@@ -405,8 +405,6 @@ install(DIRECTORY qml/keys qml/languages
 install(FILES qml/ActionsToolbar.qml qml/FloatingActions.qml qml/Keyboard.qml qml/KeyboardContainer.qml qml/WordRibbon.qml
         DESTINATION ${MALIIT_KEYBOARD_QML_DIR})
 
-install(DIRECTORY data/sounds
-        DESTINATION ${MALIIT_KEYBOARD_DATA_DIR})
 install(DIRECTORY data/themes
         DESTINATION ${MALIIT_KEYBOARD_DATA_DIR})
 install(DIRECTORY data/devices