lang/php81: Disable the libxml2 patches

Some patches were added for supporting libxml2 2.12 or newer however as
libxml2 itself has not yet been updated these patches are not compatible
with the previous versions and have runtime issues. These patches should
be added again after textproc/libxml2 has been updated to 2.12 or newer.

On the contrary if php81 has runtime issues even after the libxml2
updates and with these patches we might have to remove php81 earlier
than expected if there is no fix.

PR: 280775
Reported by: freebsdbugs@filis.org