Documentation: remove {show,whatchanged}.difftree config options

This removes, from the documentation and the bash completion script, the
two config options that were introduced by the git-whatchanged.sh script
and lost in the C rewrite. Today, we can use aliases as an alternative.

Signed-off-by: Olivier Marin <dkr@freesurf.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1007,10 +1007,6 @@ repack.usedeltabaseoffset::
 	Allow linkgit:git-repack[1] to create packs that uses
 	delta-base offset.  Defaults to false.
 
-show.difftree::
-	The default linkgit:git-diff-tree[1] arguments to be used
-	for linkgit:git-show[1].
-
 showbranch.default::
 	The default set of branches for linkgit:git-show-branch[1].
 	See linkgit:git-show-branch[1].
@@ -1075,10 +1071,6 @@ user.signingkey::
 	unchanged to gpg's --local-user parameter, so you may specify a key
 	using any method that gpg supports.
 
-whatchanged.difftree::
-	The default linkgit:git-diff-tree[1] arguments to be used
-	for linkgit:git-whatchanged[1].
-
 imap::
 	The configuration variables in the 'imap' section are described
 	in linkgit:git-imap-send[1].

contrib/completion/git-completion.bash

@@ -1041,7 +1041,6 @@ _git_config ()
 		pull.octopus
 		pull.twohead
 		repack.useDeltaBaseOffset
-		show.difftree
 		showbranch.default
 		tar.umask
 		transfer.unpackLimit
@@ -1050,7 +1049,6 @@ _git_config ()
 		user.name
 		user.email
 		user.signingkey
-		whatchanged.difftree
 		branch. remote.
 	"
 }