Rehash function table after disabling functions

Rehash function table after disabling functions

To perform fast shutdown without full table cleanup we need all
internal functions to be in one continuous chunk. This was
violated when functions were deleted via disable_functions.

This drops the zend_disable_function() API in favor of
zend_disable_functions(), which disables the given list of
functions and performs the necessary rehash afterwards.

Also drop PG(disabled_functions), which is no longer used.