gnu: perl-markdown-discount: Use a shorter patch file name.

* gnu/packages/patches/perl-text-markdown-discount-use-system-markdown.patch:
Rename to...
* gnu/packages/patches/perl-text-markdown-discount-unbundle.patch:
... this.
* gnu/packages/markup.scm (perl-text-markdown-discount): Adjust accordingly.

gnu/packages/patches/perl-text-markdown-discount-use-system-markdown.patch

@@ -1,32 +0,0 @@
-Description: Use the markdown library provided by the libmarkdown2 package.
-Author: Alessandro Ghedini <al3xbio@gmail.com>
-Origin: vendor
-Forwarded: not-needed
-Last-Update: 2012-01-01
-
---- a/Makefile.PL
-+++ b/Makefile.PL
-@@ -57,12 +57,6 @@
- 
- 
- 
--sub MY::postamble {
--    return sprintf('
--$(MYEXTLIB):
--	%s
--', qq{( cd $extdir; CC='cc -fPIC' sh configure.sh; make )\n});
--}
- 
- WriteMakefile(
-     NAME              => 'Text::Markdown::Discount',
-@@ -71,8 +65,6 @@
-     ($] >= 5.005 ?
-       (ABSTRACT_FROM  => 'lib/Text/Markdown/Discount.pm',
-        AUTHOR         => 'Masayoshi Sekimura <sekimura@cpan.org>') : ()),
--    LIBS               => '-L' . $extdir,
--    INC               => '-I. -I' . $extdir,
--    MYEXTLIB          => $myextlib,
--    clean             => { FILES => $clean_files },
-+    LIBS               => '-lmarkdown',
-+    INC               => '-I.',
- );