Tidy the Pod exclusion rules in buildtoc.

Tidy the Pod exclusion rules in buildtoc.

The rule to skip lib/Attribute/Handlers/demo/ was added by commit
a83b6f4664409877 in June 2001, and rendered obsolete when Attribute:Handlers
was moved to ext/ with commit 261f6fe66fcb39f4 in February 2009.
The rule to skip Deve::PPPort's harness was added by commit 428dc699a4f0702c
and tweaked by commit 34babc168865edbd, both in November 2001.
It was rendered obsolete when the harness was merged into the main
Devel::PPPort code in commit 4428420042d0cf28 in December 2001.
The rule to skip Math::BitInt's tests, added in commit ba62762e535f4b26 in
November 2001 was made superfluous when the general rule to skip test
directories was added by commit 2a55110093932342 in May 2003.