unify textual licence description under <availability>

[haoess]

The attached patch unifies the textual licence description under //availability as licence, (no more switch between //availability/licence and //availability/p).

diff --git a/mets_mods2tei/api/tei.py b/mets_mods2tei/api/tei.py
index 29c27e5..55a46e6 100644
--- a/mets_mods2tei/api/tei.py
+++ b/mets_mods2tei/api/tei.py
@@ -435,25 +435,23 @@ class Tei:
         else:
             availability = etree.SubElement(publication_stmt, "%savailability" % TEI)

+        licence = etree.SubElement(availability, "%slicence" % TEI)
         # an explicit licence has been set
         if status == "licence" and licence_text != "":
             availability.set("status", "licenced")
-            licence = etree.SubElement(availability, "%slicence" % TEI)
             licence.text = licence_text
             if licence_url != "":
                 licence.set("target", licence_url)
         # public domain
         elif status == "free":
-            note = etree.SubElement(availability, "%sp" % TEI)
-            note.text = "In the public domain"
+            licence.text = "In the public domain"
             availability.set("status", "free")
         elif status == "unknown":
             availability.set("status", "unknown")
         # use restricted as default
         else:
             availability.set("status", "restricted")
-            note = etree.SubElement(availability, "%sp" % TEI)
-            note.text = "Available under licence from the publishers."
+            licence.text = "Available under licence from the publishers."

     def add_encoding_date(self, date):
         """