Dpkg::Changelog::Entry::Debian: Remove non-functional timezone name support

The Debian changelog trailer regex intended to support a timezone name
inside parenthesis, like this:

 -- Name <mail@example.org>  Sat, 30 May 2015 03:18:43 +0200 (CEST)

is bogus, and it only accepts one character. As in:

 -- Name <mail@example.org>  Sat, 30 May 2015 03:18:43 +0200 (C)

which while also "valid", as per RFC822, they are pretty much useless
as per RFC5322. The implementation has kept that part unchanged since
its inception in dpkg 1.3.0, 1996-08.

So let's just drop it instead of fixing the regex, given that the
timezone name has never been accepted, many time-parsing functions
ignore it, it is redundant, declared obsolete by RFC5322 and Debian
policy dropped an explicit reference to it due to bug #569174.

debian/changelog

@@ -2,6 +2,9 @@ dpkg (1.18.2) UNRELEASED; urgency=low
 
   [ Guillem Jover ]
   * Fix plural form translations for single plural languages. Closes: #790025
+  * Perl modules:
+    - Remove non-functional timezone name support from
+      Dpkg::Changelog::Entry::Debian.
   * Documentation:
     - Fix grammar in dpkg-architecture(1).
       Thanks to Chris Lamb <lamby@debian.org>. Closes: #787616

scripts/Dpkg/Changelog/Entry/Debian.pm

@@ -64,7 +64,7 @@ our $regex_header = qr/^(\w$name_chars*) \(([^\(\) \t]+)\)((?:\s+$name_chars+)+)
 
 # The matched content is the maintainer name ($1), its email ($2),
 # some blanks ($3) and the timestamp ($4).
-our $regex_trailer = qr/^ \-\- (.*) <(.*)>(  ?)((\w+\,\s*)?\d{1,2}\s+\w+\s+\d{4}\s+\d{1,2}:\d\d:\d\d\s+[-+]\d{4}(\s+\([^\\\(\)]\))?)\s*$/o;
+our $regex_trailer = qr/^ \-\- (.*) <(.*)>(  ?)((\w+\,\s*)?\d{1,2}\s+\w+\s+\d{4}\s+\d{1,2}:\d\d:\d\d\s+[-+]\d{4})\s*$/o;
 
 ## use critic