DEPL — Dangling references to "label" attribute

In the adopted specification, some classes used "label" attributes
for identification purposes to support traceability. Issue 5964
changed these classes to have "name" instead of "label" attributes.
However, some references to the "label" attributes still exist in
the document.

Proposed resolution:

In section 6.4.9.1, remove the paragraph that reads

A label can optionally be associated with the AssemblyCon-
nectionDescription. Assembly design tools might use this label
to visualize the connection.

In section 6.8.3.1, change the fifth sentence of the first paragraph
from

The MonolithicDeploymentDescription contains a human-readable
label and references ArtifactDeploymentDescription elements for
all artifacts that are part of the deployment.

to read

The MonolithicDeploymentDescription references ArtifactDeploy-
mentDescription elements for all artifacts that are part of
the deployment.

In section 6.11.1.1, update the diagram for the PackageError
exception.