Properly remove all attributes when unserializing HTML from the existin

HTML, HEAD and BODY tags

src/pyj/dom.pyj

@@ -59,12 +59,21 @@ def build_rule(selector, **kw):
     ans.push('}')
     return ans.join('\n') + '\n'
 
+
 def clear():
     for v'var i = 0; i < arguments.length; i++':
         node = arguments[i]
         while node.firstChild:
             node.removeChild(node.firstChild)
 
+
+def remove_all_attributes():
+    for v'var i = 0; i < arguments.length; i++':
+        node = arguments[i]
+        while node.attributes.length > 0:
+            node.removeAttribute(node.attributes[0].name)
+
+
 def create_keyframes(animation_name, *frames):
     ans = v'[]'
     for prefix in '-webkit-', '-moz-', '-o-', '':

src/pyj/read_book/resources.pyj

@@ -5,7 +5,7 @@ from __python__ import hash_literals
 from elementmaker import E
 from encodings import base64decode, utf8_decode
 
-from dom import clear
+from dom import clear, remove_all_attributes
 from read_book.globals import ui_operations
 
 JSON_XHTML_MIMETYPE = 'application/calibre+xhtml+json'
@@ -228,9 +228,11 @@ def unserialize_html(serialized_data, proceed, postprocess_dom):
     tree = serialized_data.tree
     ns_map = serialized_data.ns_map
     html = tag_map[0]
+    remove_all_attributes(document.documentElement)
     apply_attributes(html, document.documentElement, ns_map)
     head, body = tree[1], tree[2]  # noqa: unused-local
     clear(document.head, document.body)
+    remove_all_attributes(document.head, document.body)
     # Default stylesheet
     document.head.appendChild(E.style(type='text/css', 'html {{ font-family: {} }}'.format(window.default_font_family or "sans-serif")))
     resource_urls = {}