send-email: avoid duplicate specification warnings

A warning is issued for options which are specified more than once
beginning with perl-Getopt-Long >= 2.55.  In addition to causing users
to see warnings, this results in test failures which compare the output.
An example, from t9001-send-email.37:

  | +++ diff -u expect actual
  | --- expect      2023-11-14 10:38:23.854346488 +0000
  | +++ actual      2023-11-14 10:38:23.848346466 +0000
  | @@ -1,2 +1,7 @@
  | +Duplicate specification "no-chain-reply-to" for option "no-chain-reply-to"
  | +Duplicate specification "to-cover|to-cover!" for option "to-cover"
  | +Duplicate specification "cc-cover|cc-cover!" for option "cc-cover"
  | +Duplicate specification "no-thread" for option "no-thread"
  | +Duplicate specification "no-to-cover" for option "no-to-cover"
  |  fatal: longline.patch:35 is longer than 998 characters
  |  warning: no patches were sent
  | error: last command exited with $?=1
  | not ok 37 - reject long lines

Remove the duplicate option specs.  These are primarily the explicit
'--no-' prefix opts which were added in f471494 (git-send-email.perl:
support no- prefix with older GetOptions, 2015-01-30).  This was done
specifically to support perl-5.8.0 which includes Getopt::Long 2.32[1].

Getopt::Long 2.33 added support for the '--no-' prefix natively by
appending '!' to the option specification string, which was included in
perl-5.8.1 and is not present in perl-5.8.0.  The previous commit bumped
the minimum supported Perl version to 5.8.1 so we no longer need to
provide the '--no-' variants for negatable options manually.

Teach `--git-completion-helper` to output the '--no-' options.  They are
not included in the options hash and would otherwise be lost.

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

git-send-email.perl

@@ -119,13 +119,16 @@ sub completion_helper {
 
 	foreach my $key (keys %$original_opts) {
 		unless (exists $not_for_completion{$key}) {
-			$key =~ s/!$//;
+			my $negatable = ($key =~ s/!$//);
 
 			if ($key =~ /[:=][si]$/) {
 				$key =~ s/[:=][si]$//;
 				push (@send_email_opts, "--$_=") foreach (split (/\|/, $key));
 			} else {
 				push (@send_email_opts, "--$_") foreach (split (/\|/, $key));
+				if ($negatable) {
+					push (@send_email_opts, "--no-$_") foreach (split (/\|/, $key));
+				}
 			}
 		}
 	}
@@ -491,7 +494,6 @@ sub config_regexp {
 		    "bcc=s" => \@getopt_bcc,
 		    "no-bcc" => \$no_bcc,
 		    "chain-reply-to!" => \$chain_reply_to,
-		    "no-chain-reply-to" => sub {$chain_reply_to = 0},
 		    "sendmail-cmd=s" => \$sendmail_cmd,
 		    "smtp-server=s" => \$smtp_server,
 		    "smtp-server-option=s" => \@smtp_server_options,
@@ -506,36 +508,27 @@ sub config_regexp {
 		    "smtp-auth=s" => \$smtp_auth,
 		    "no-smtp-auth" => sub {$smtp_auth = 'none'},
 		    "annotate!" => \$annotate,
-		    "no-annotate" => sub {$annotate = 0},
 		    "compose" => \$compose,
 		    "quiet" => \$quiet,
 		    "cc-cmd=s" => \$cc_cmd,
 		    "header-cmd=s" => \$header_cmd,
 		    "no-header-cmd" => \$no_header_cmd,
 		    "suppress-from!" => \$suppress_from,
-		    "no-suppress-from" => sub {$suppress_from = 0},
 		    "suppress-cc=s" => \@suppress_cc,
 		    "signed-off-cc|signed-off-by-cc!" => \$signed_off_by_cc,
-		    "no-signed-off-cc|no-signed-off-by-cc" => sub {$signed_off_by_cc = 0},
-		    "cc-cover|cc-cover!" => \$cover_cc,
-		    "no-cc-cover" => sub {$cover_cc = 0},
-		    "to-cover|to-cover!" => \$cover_to,
-		    "no-to-cover" => sub {$cover_to = 0},
+		    "cc-cover!" => \$cover_cc,
+		    "to-cover!" => \$cover_to,
 		    "confirm=s" => \$confirm,
 		    "dry-run" => \$dry_run,
 		    "envelope-sender=s" => \$envelope_sender,
 		    "thread!" => \$thread,
-		    "no-thread" => sub {$thread = 0},
 		    "validate!" => \$validate,
-		    "no-validate" => sub {$validate = 0},
 		    "transfer-encoding=s" => \$target_xfer_encoding,
 		    "format-patch!" => \$format_patch,
-		    "no-format-patch" => sub {$format_patch = 0},
 		    "8bit-encoding=s" => \$auto_8bit_encoding,
 		    "compose-encoding=s" => \$compose_encoding,
 		    "force" => \$force,
 		    "xmailer!" => \$use_xmailer,
-		    "no-xmailer" => sub {$use_xmailer = 0},
 		    "batch-size=i" => \$batch_size,
 		    "relogin-delay=i" => \$relogin_delay,
 		    "git-completion-helper" => \$git_completion_helper,