[TINY] Remove import to the disappeared XMPPFramework.h.

Many extensions import `XMPPFramework.h`, but they don't really need it.

The commit removes those references (or changes it to the `XMPP.h`) while the projects still compile (tested including the extensions I modified in the iPhone and Mac sample).

I “needed” this change, since in the project I was using XMPPFramework there wasn’t a `XMPPFramework.h` (we use a different name), but the include path happens to add `XMPPFramework/Xcode` folder recursively. This actually imports a `XMPPFramework.h` from the examples, which has `XMPPCapabilites.h` included, which we don’t use in the real project. A dummy `XMPPFramework.h` will work as a workaround, but we think that the framework files should not depend on a “consumer” provided header.