git-config.1: --get-all description update

"git config --get-all foo.bar" shows all values for the foo.bar
variable, but does not give the variable name in each output entry.
Hence it is equivalent to "git config get --all foo.bar", without
"--show-names", in the more modern syntax.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: gitster

Documentation/git-config.txt

@@ -309,7 +309,7 @@ recommended to migrate to the new syntax.
 	Replaced by `git config get [--value=<pattern>] <name>`.
 
 --get-all <name> [<value-pattern>]::
-	Replaced by `git config get [--value=<pattern>] --all --show-names <name>`.
+	Replaced by `git config get [--value=<pattern>] --all <name>`.
 
 --get-regexp <name-regexp>::
 	Replaced by `git config get --all --show-names --regexp <name-regexp>`.