diff-tree doc: correct & remove wrong documentation

The documentation saying that diff-tree didn't support anything except
literal prefixes hasn't been true since
d38f2809 ("tree_entry_interesting(): support wildcard matching",
2010-12-15), but this documentation was not updated at the time.

Since this command uses pathspecs like most other commands, there's no
need to show examples of how the various "cmd <revs> <paths>"
invocations work.

Furthermore, the "git diff-tree --abbrev 5319e4" example shown here
never worked. We'd ended up with that through a combination of
62b42d34 ("docs: fix some antique example output", 2011-05-26) and
ac4e0869 ("Adjust core-git documentation to more recent Linus GIT.",
2005-05-05), but "git diff-tree <tree>" was always invalid.
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-diff-tree.txt

@@ -31,10 +31,7 @@ include::diff-options.txt[]
 
 <path>...::
 	If provided, the results are limited to a subset of files
-	matching one of these prefix strings.
-	i.e., file matches `/^<pattern1>|<pattern2>|.../`
-	Note that this parameter does not provide any wildcard or regexp
-	features.
+	matching one of the provided pathspecs.
 
 -r::
         recurse into sub-trees
@@ -114,52 +111,6 @@ include::pretty-options.txt[]
 
 
 include::pretty-formats.txt[]
-
-
-LIMITING OUTPUT
----------------
-If you're only interested in differences in a subset of files, for
-example some architecture-specific files, you might do:
-
-	git diff-tree -r <tree-ish> <tree-ish> arch/ia64 include/asm-ia64
-
-and it will only show you what changed in those two directories.
-
-Or if you are searching for what changed in just `kernel/sched.c`, just do
-
-	git diff-tree -r <tree-ish> <tree-ish> kernel/sched.c
-
-and it will ignore all differences to other files.
-
-The pattern is always the prefix, and is matched exactly.  There are no
-wildcards.  Even stricter, it has to match a complete path component.
-I.e. "foo" does not pick up `foobar.h`.  "foo" does match `foo/bar.h`
-so it can be used to name subdirectories.
-
-An example of normal usage is:
-
-  torvalds@ppc970:~/git> git diff-tree --abbrev 5319e4
-  :100664 100664 ac348b... a01513...	git-fsck-objects.c
-
-which tells you that the last commit changed just one file (it's from
-this one:
-
------------------------------------------------------------------------------
-commit 3c6f7ca19ad4043e9e72fa94106f352897e651a8
-tree 5319e4d609cdd282069cc4dce33c1db559539b03
-parent b4e628ea30d5ab3606119d2ea5caeab141d38df7
-author Linus Torvalds <torvalds@ppc970.osdl.org> Sat Apr 9 12:02:30 2005
-committer Linus Torvalds <torvalds@ppc970.osdl.org> Sat Apr 9 12:02:30 2005
-
-Make "git-fsck-objects" print out all the root commits it finds.
-
-Once I do the reference tracking, I'll also make it print out all the
-HEAD commits it finds, which is even more interesting.
------------------------------------------------------------------------------
-
-in case you care).
-
-
 include::diff-format.txt[]
 
 GIT