Reduce content model in screen

[ghost]

Problem Description

This is valid:

<screen><literal># eon resource-update &lt;RESOURCE_ID&gt; [...]</literal></screen> 

(This is autoconverted stuff from the Cloud docs, that is the only reason why it exists...)

Expected Behavior

It should not be valid because it makes no sense and can create Novdoc conversion issues.

[ghost]

A list of stuff that reasonably should be allowed (cf.):

(text)
co
code
command
constant
email
emphasis
envar
filename
footnote
option
package
parameter
phrase
prompt
property
remark
replaceable
systemitem
tag
type
uri
varname

[tomschr]

@sknorr The element type was already declared as "not allowed" so I'll remove it from the list.

[ghost]

Right -- that was just an oversight on my part. Shouldn't have been on the list in the first place. Thanks for noticing.