Remove the documentation for the <s-x> keybinding

It was removed in commit 0e1632868e0377caf50db5d7e2361b7477533a9b and it
is now the standard kill-region command.
Remove the documentation for the <s-g> keybinding

It was removed in commit d49a8e9a16e2b3dacd55b4de3e526405cec6e13d and it
is now bound to the god-local-mode command.
Remove two keybinding tips concerning Super

- <s-f> was removed in commit d49a8e9a16e2b3dacd55b4de3e526405cec6e13d.
- <s-m> was removed in commit 0e1632868e0377caf50db5d7e2361b7477533a9b.
Merge pull request #642 from tow8ie/remove-old-keymap-documentation

Remove old keymap documentation
Turn on electric indent mode with python mode
Automatically newline with block start
Insert magic encoding comment upon save
Merge pull request #644 from toctan/python

Better python mode defaults
Update documentation and tips for projectile keys
Merge pull request #646 from hron/update-documentation-for-projectile-keys

Update documentation and tips for projectile keys
Added M-X to README [Close #621]
Merge pull request #649 from k1-hedayati/update-readme-for-smex-major-mode-binding

Added M-X to README
Merge branch 'master' into personal

* master:
  Added M-X to README [Close #621]
  Update documentation and tips for projectile keys
  Insert magic encoding comment upon save
  Automatically newline with block start
  Turn on electric indent mode with python mode
  Remove two keybinding tips concerning Super
  Remove the documentation for the <s-g> keybinding
  Remove the documentation for the <s-x> keybinding