Revert "Emable overriding the email template."

Dependencies

• [2] BXW62TGJ Emable overriding the email template.
• [3] QDJRQIFF If multiple dependent builds fail, send a single email
• [4] RPTSGIRC Eliminate duplicate getPreviousBuild functions
• [5] ZEDMA4P6 Handle HYDRA_EMAIL_TEMPLATES that are paths
• [6] LDICTHWY Use Template::Toolkit to generate email messages
• [*] 5EQYVRWE Add a plugin mechanism

Change contents

• replacement in src/lib/Hydra/Plugin/EmailNotification.pm at line 17
  [3.39]→[2.0:54](∅→∅)
  − my $template = $ENV{'HYDRA_EMAIL_TEMPLATE'} || <<EOF;
  [3.39]

  [3.472]
  + my $template = <<EOF;