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 <[email protected]>
Signed-off-by: Felipe Contreras <[email protected]>

git-fc 0.1