maint: get rid of $perllibdir environment variable hack

maint: get rid of $perllibdir environment variable hack

That was needed when the automake-$APIVERSION and aclocal-$APIVERSION
wrapper scripts used by the testsuite were shell script, rather than
perl scripts acting as a thin layers.

* aclocal.in (BEGIN): Update @INC based on the contents of the array
'@Aclocal::perl_libdirs', rather than of the environment variable
'perllibdir'.
* t/wrap/aclocal.in (BEGIN): Initialize '@Aclocal::perl_libdirs'
rather than $ENV{'perllibdir'}.
* automake.in (BEGIN): Update @INC based on the contents of the array
'@Automake::perl_libdirs', rather than of the environment variable
'perllibdir'.
* t/wrap/automake.in (BEGIN): Initialize '@Automake::perl_libdirs'
rather than $ENV{'perllibdir'}.
* NEWS: Update.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>