Pod-Perldoc: exclude corpus files that are not used for anything

The Pod-Perldoc distribution includes several files in its corpus
directory but which aren't used for anything. They appear to be for
manual testing. There is little reason to include them in core.
Additionally, one of the files included is an old copy of perlfunc.pod,
which continually confuses contributors to core.

MANIFEST

@@ -1802,9 +1802,6 @@ cpan/Pod-Escapes/lib/Pod/Escapes.pm	Pod::Escapes
 cpan/Pod-Escapes/t/01_about_verbose.t	test Pod::Escapes
 cpan/Pod-Escapes/t/10_main.t		test Pod::Escapes
 cpan/Pod-Escapes/t/15_name2charnum.t	test Pod::Escapes
-cpan/Pod-Perldoc/corpus/no-head.pod		test file for Pod-Perldoc
-cpan/Pod-Perldoc/corpus/perlfunc.pod		test file for Pod-Perldoc
-cpan/Pod-Perldoc/corpus/utf8.pod		test file for Pod-Perldoc
 cpan/Pod-Perldoc/lib/Pod/Perldoc.pm		guts of the 'perldoc' utility
 cpan/Pod-Perldoc/lib/Pod/Perldoc/BaseTo.pm	utility module for perldoc
 cpan/Pod-Perldoc/lib/Pod/Perldoc/GetOptsOO.pm	options parsing for perldoc

Porting/Maintainers.pl

@@ -956,6 +956,9 @@ package Maintainers;
             # utils first
             'perldoc',
 
+            # files only used for manual testing
+            qr[^corpus/],
+
             # https://rt.cpan.org/Ticket/Display.html?id=116827
             't/02_module_pod_output.t'
         ],