tools: fix constructing XML by dropping broken pretty_xml()

I don't understand the code, but it mangles the XML.

There is no difference in the markup we have so far. But if you
have nested XML (like for description-docbook tag) there are cases
where this is wrong.

There is also no need to prettify anything. If you want pretty-formatted
XML, do it yourself, for example with

  $ tidy --indent yes --indent-spaces 4 --indent-attributes yes --wrap-attributes yes --input-xml yes --output-xml yes src/libnm-client-impl/nm-property-infos-nmcli.xml

I think this was initially done, because we had the tool in perl, and
when migrating, we wanted to generate the exactly same output. And it
was the same output, and it was fine for the input we have. But with
different input, it's wrong. Drop it now.

tools/generate-docs-nm-property-infos.py

@@ -123,18 +123,6 @@ def write_data(setting_node, parsed_data):
         property_node.append(des)
 
 
-def pretty_xml(element, newline, level=0):
-    if element:
-        if (element.text is None) or element.text.isspace():
-            element.text = newline
-        else:
-            element.text = newline + element.text.strip() + newline
-    temp = list(element)
-    for subelement in temp:
-        subelement.tail = newline
-        pretty_xml(subelement, newline, level=level + 1)
-
-
 if len(sys.argv) < 4:
     print("Usage: %s [plugin] [output-xml-file] [srcfiles]" % (sys.argv[0]))
     exit(1)
@@ -152,6 +140,4 @@ for one_file in source_files:
         setting_node.text = "\n"
         scan_doc_comments(plugin, setting_node, one_file, start_tag, end_tag)
 
-pretty_xml(root_node, "\n")
-
 ET.ElementTree(root_node).write(output)