Remove NDEBUG constant

[Girgias]

It was only used in our patched libmagic in a very convoluted way.

The PHP_DEBUG and ZEND_DEBUG constants are always defined and should be used instead.

I came across this while working on #5526

[nikic]

NDEBUG is a standard C constant, I don't think we should drop it. This will break code using assert() rather than ZEND_ASSERT for example.

[Girgias]

NDEBUG is a standard C constant, I don't think we should drop it. This will break code using assert() rather than ZEND_ASSERT for example.

TIL, should I keep the libmagic change and drop the rest?

[nikic]

I'd prefer leaving libmagic alone as well, because #ifndef NDEBUG around variables used only in assert() is also a standard pattern.

[Girgias]

I'd prefer leaving libmagic alone as well, because #ifndef NDEBUG around variables used only in assert() is also a standard pattern.

ACK