Avoid loading many unneeded assemblies on start

Author: davidebbo

src/WebJobs.Script.WebHost/Web.config

@@ -14,7 +14,17 @@
       </system.Web>
   -->
   <system.web>
-    <compilation debug="true" targetFramework="4.6" />
+    <compilation debug="true" targetFramework="4.6">
+      <assemblies>
+        <clear />
+        <add assembly="Microsoft.Azure.WebJobs.Script.WebHost" />
+      </assemblies>
+    </compilation>
+    <pages>
+      <namespaces>
+        <clear />
+      </namespaces>
+    </pages>
     <httpRuntime targetFramework="4.5" maxRequestLength="16384" />
   </system.web>
   <system.webServer>