difftool: eliminate setup_environment function

Removing this function shortens the code and makes it easier to read.
Now all environment variables are set as part of procedural operation.

Signed-off-by: Tim Henigan <tim.henigan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-difftool.perl

@@ -29,12 +29,6 @@ USAGE
 	exit($exitcode);
 }
 
-sub setup_environment
-{
-	$ENV{GIT_PAGER} = '';
-	$ENV{GIT_EXTERNAL_DIFF} = 'git-difftool--helper';
-}
-
 # parse command-line options. all unrecognized options and arguments
 # are passed through to the 'git diff' command.
 my ($difftool_cmd, $extcmd, $gui, $help, $prompt);
@@ -79,7 +73,8 @@ if (defined($prompt)) {
 	}
 }
 
-setup_environment();
+$ENV{GIT_PAGER} = '';
+$ENV{GIT_EXTERNAL_DIFF} = 'git-difftool--helper';
 my @command = ('git', 'diff', @ARGV);
 
 # ActiveState Perl for Win32 does not implement POSIX semantics of