difftool: remove angular brackets from argument help

Parseopt wraps arguments in a pair of angular brackets by default,
signifying that the user needs to replace it with a value of the
documented type.  Remove the pairs from the option definitions to
duplication and confusion.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/difftool.c

@@ -703,7 +703,7 @@ int cmd_difftool(int argc, const char **argv, const char *prefix)
 			NULL, 1 },
 		OPT_BOOL(0, "symlinks", &symlinks,
 			 N_("use symlinks in dir-diff mode")),
-		OPT_STRING('t', "tool", &difftool_cmd, N_("<tool>"),
+		OPT_STRING('t', "tool", &difftool_cmd, N_("tool"),
 			   N_("use the specified diff tool")),
 		OPT_BOOL(0, "tool-help", &tool_help,
 			 N_("print a list of diff tools that may be used with "
@@ -711,7 +711,7 @@ int cmd_difftool(int argc, const char **argv, const char *prefix)
 		OPT_BOOL(0, "trust-exit-code", &trust_exit_code,
 			 N_("make 'git-difftool' exit when an invoked diff "
 			    "tool returns a non - zero exit code")),
-		OPT_STRING('x', "extcmd", &extcmd, N_("<command>"),
+		OPT_STRING('x', "extcmd", &extcmd, N_("command"),
 			   N_("specify a custom command for viewing diffs")),
 		OPT_END()
 	};