Remove diff_method option

Our built-in "diff"-like functionality is pretty good because it's aware of
beets' data structures and types. This makes it more legible, in my opinion,
than an ordinary textual diff. So for now, I'm making this the only option (in
the spirit of making the plugin as straightforward as humanly possible).

beetsplug/edit.py

@@ -40,7 +40,6 @@ class EditPlugin(plugins.BeetsPlugin):
 
         self.config.add({
             'editor': '',
-            'diff_method': '',
             'browser': '',
             'albumfields': 'album albumartist',
             'itemfields': 'track title artist album',
@@ -55,14 +54,6 @@ class EditPlugin(plugins.BeetsPlugin):
         # your htmlviewer. Defaults to open with webrowser module
         self.browser = self.config['browser'].as_str_seq()
 
-        # the diff_method field in your config picks the way to see your
-        # changes. Options are:
-        # 'ndiff'(2 files with differences),
-        # 'unified'(just the different lines and a few lines of context),
-        # 'html'(view in html-format),
-        # 'vimdiff'(view in VIM)
-        self.diff_method = self.config['diff_method'].get(unicode)
-
         # the albumfields field in your config sets the tags that
         # you want to see/change for albums.
         # Defaults to album albumartist.
@@ -116,13 +107,6 @@ class EditPlugin(plugins.BeetsPlugin):
             self.brw_args = self.browser[1:] if len(self.browser) > 1 else None
             self.brw = self.browser[0] if self.browser else None
 
-        # 4 ways to view the changes in objects
-        self.diffresults = {
-            'ndiff': self.ndiff,
-            'unified': self.unified,
-            'html': self.html,
-            'vimdiff': self.vimdiff}
-
         # main program flow
         # Get the objects to edit.
         query = decargs(args)
@@ -296,14 +280,11 @@ class EditPlugin(plugins.BeetsPlugin):
             ob.update(n[1])  # update the object
             newSetTitled.append((format(ob),) + n[1:])
             changedObjs.append(ob)
+
         # see the changes we made
-        if self.diff_method:
-            ostr = self.print_to_yaml(oldSetTitled)
-            nwstr = self.print_to_yaml(newSetTitled)
-            self.diffresults[self.diff_method](ostr, nwstr)
-        else:
-            for obj in changedObjs:
-                ui.show_model_changes(obj)
+        for obj in changedObjs:
+            ui.show_model_changes(obj)
+
         self.save_write(changedObjs)
 
     def save_write(self, changedob):

docs/plugins/edit.rst

@@ -52,7 +52,6 @@ Make a ``edit:`` section in your config.yaml ``(beet config -e)``
 
     edit:
        editor: nano -w -p
-       diff_method: html
        browser: firefox  -private-window
        albumfields: genre album
        itemfields: track artist
@@ -61,12 +60,6 @@ Make a ``edit:`` section in your config.yaml ``(beet config -e)``
 
 * ``editor:`` pick your own texteditor; add arguments if needed. If no``editor:`` then your system opens the file-extension.
 
-* ``diff_method:`` 4 choices. With no ``diff_method:`` you get the beets way of showing differences.
-    - ``ndiff``: you see original and the changed yamls with the changes.
-    - ``unified``: you see the changes with a bit of context. Simple and compact.
-    - ``html``: a html file that you can open in a browser. Looks nice.
-    - ``vimdiff``: gives you VIM with the diffs.You need VIM for this.
-
 * ``browser:``
   If you pick ``diff_method:html`` you can specify a viewer for it (if needed add arguments). If not, let your system open the file-extension.