In makedef.pl, remove PL_csh{len,name} from 3 skip lists.

In makedef.pl, remove PL_csh{len,name} from 3 skip lists.

PL_cshname was converted to a true global by commit 618b9757aa96db62 in
2007, and PL_cshlen to a constant macro. Effectively both were dropped from
the list of exported symbols at this time, although as they were skipped on
Win32, WinCE and NetWare, the only platforms which would have noticed would
be AIX, OS/2 and VMS. As they've been missing in 5.10.0, 5.12.0 and 5.14.0
without any bug reports, it doesn't seem worth re-adding PL_cshname to the
list of exported symbols.