Remove the Calendar portlet.

Drops dependency on calendar portlet 2.1.3-M4, removing it from the `pom.xml`, dropping the overlay upon it, and removing the portlet publication and layout reference to it.  This allows the uPortal build to succeed despite the calendar portlet's caldav4j dependency not yet being available in Central and no longer being available in third party repo.

See also 
* uportal-user@ [thread](http://thread.gmane.org/gmane.comp.java.jasig.uportal/16917).
* uportal-dev@ [thread](http://thread.gmane.org/gmane.comp.java.jasig.uportal.devel/5596).

## Before this change:

```
$ mvn clean package
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5:01.746s
[INFO] Finished at: Tue Mar 11 10:22:25 CDT 2014
[INFO] Final Memory: 84M/508M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal on project CalendarPortlet: Could not resolve dependencies for project org.jasig.portal.portlets-overlay:CalendarPortlet:war:4.1.0-SNAPSHOT: Failed to collect dependencies at org.jasig.portlet:CalendarPortlet:jar:classes:2.1.3-M4 -> org.osaf:caldav4j:jar:0.7 -> xalan:serializer:jar:2.7.0: Failed to read artifact descriptor for xalan:serializer:jar:2.7.0: Could not transfer artifact xalan:serializer:pom:2.7.0 from/to osafoundation.org (http://builds.osafoundation.org/maven2): Connection to http://builds.osafoundation.org refused: Connection refused -> [Help 1]
```

## With this change
...
```
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
```

This is intended as a temporary fix allowing the uPortal build to succeed where the local mvn repository is not pre-populated with .jars not available from Central.  The Calendar portlet's dependencies can be published to Central via [the process for submitting third party dependencies](https://docs.sonatype.org/display/Repository/Uploading+3rd-party+Artifacts+to+The+Central+Repository), and ideally the Calendar portlet could be release engineered to [no longer reference third party Maven repositories](https://github.com/Jasig/CalendarPortlet/blob/55b4d9aaf038a6b4402f7aa06269a8e3990880c6/pom.xml#L31) and to be available in a GA release rather than milestone release version, at which point it would be appropriate to re-add the Calendar portlet to uPortal's out-of-the-box Quickstart build.