Little clean-up on php.mk

[pizzamig]

Summary

php.mk is still referring to some not-existant extensions, like ncurses, sqlite, oci8.
Moreover, spl is not built as extension (the port doesn't exist) and is treated like pcre.
Converted if ${PHP_VER} == 70 || ${PHP_VER} == 71 || ${PHP_VER} == 72 as if ${PHP_VER} >= 70
improving uniformity

[ale]

spl is treated exactly as pcre, they are two always-on extensions. Why would you remove one and not the other? Removing it would break all ports that explicitly depends on it (USE_PHP=spl). Even if it's currently enabled by default, its explicit dependency allows for newer php versions to have it as a module without any change to other ports.

[pizzamig]

Put spl back to _USE_PHP_ALL, as it correctly belongs.
Sorry for the poor word choice, I wanted only remove the DEPENDS line
that refer to a package that doesn't exist.