DDSJAVA11 — ModifiableInstanceHandle should be removed

The ModifiableInstanceHandle was not removed along with all other modifiable types.
As such it should be removed for consistency, useability and performances.

Specificaly the following methods should be removed:

• ServiceEnvironment.newInstanceHandle()
• DataReader.lookupInstance(ModifiableInstanceHandle handle, TYPE keyHolder)
• DataWriter.lookupInstance(ModifiableInstanceHandle handle, TYPE keyHolder)

And the following method should be modified to return InstanceHandle:

• Sample.getInstanceHandle()
• Sample.getPublicationHandle()

Notice: the returning ModifialbeInstanceHandle forces defensive copying with obvious consequences in term of performances.