Remove datagrid as a singleton

dev_mode/package.json

@@ -170,7 +170,6 @@
     "@phosphor/application": "^1.7.0",
     "@phosphor/commands": "^1.7.0",
     "@phosphor/coreutils": "^1.3.1",
-    "@phosphor/datagrid": "^0.1.11",
     "@phosphor/disposable": "^1.3.0",
     "@phosphor/domutils": "^1.1.3",
     "@phosphor/dragdrop": "^1.3.0",
@@ -254,7 +253,6 @@
       "@phosphor/application",
       "@phosphor/commands",
       "@phosphor/coreutils",
-      "@phosphor/datagrid",
       "@phosphor/disposable",
       "@phosphor/domutils",
       "@phosphor/dragdrop",