qbs project: Fix another duplicate dependency

Change-Id: Id50643364b174e150666f4591fa6eaf91144336b
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/plugins/help/help.qbs

@@ -5,7 +5,7 @@ import "../QtcPlugin.qbs" as QtcPlugin
 QtcPlugin {
     name: "Help"
 
-    Depends { name: "Qt"; submodules: ["core", "help", "network", "webkit"]; }
+    Depends { name: "Qt"; submodules: ["help", "network", "webkit"]; }
     Depends {
         condition: Qt.core.versionMajor >= 5;
         name: "Qt"; submodules: ["printsupport", "webkitwidgets"];