coloque \.php$ entre aspas duplas
<FilesMatch "\.php$">
SetHandler application/x-httpd-php
</FilesMatch>
reiniciar apache2 :
sudo service apache2 restart
se isso não resolver o problema, altere FilesMatch para LocationMatch e reinicie apache2
<LocationMatch "\.php$">
SetHandler application/x-httpd-php
</LocationMatch>