hash-object doc: stop mentioning git-cvsimport

Remove a reference to git-cvsimport in the intro. As can be seen from
the history of this command[1] it was originally intended for use with
git-cvsimport, but how it uses it (and that it uses it at all) is
irrelevant trivia at this point.

1. See 7672db2 ("[PATCH] Expose object ID computation functions.",
   2005-07-08) and 8b8840e ("[PATCH] cvsgit fixes: spaces in
   filenames and CVS server dialog woes", 2005-08-15).

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

Documentation/git-hash-object.txt

@@ -18,9 +18,7 @@ Computes the object ID value for an object with specified type
 with the contents of the named file (which can be outside of the
 work tree), and optionally writes the resulting object into the
 object database.  Reports its object ID to its standard output.
-This is used by 'git cvsimport' to update the index
-without modifying files in the work tree.  When <type> is not
-specified, it defaults to "blob".
+When <type> is not specified, it defaults to "blob".
 
 OPTIONS
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