Clean up includes of PHP API headers

Eliminate redundant and unused includes.

Only include the minimum headers needed before the PHP_MAJOR_VERSION
check in case future PHP versions remove some of the headers we
include.

Lib/php/phprun.swg

@@ -9,16 +9,15 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-#include "zend.h"
-#include "zend_API.h"
-#include "zend_exceptions.h"
+
 #include "php.h"
 
 #if PHP_MAJOR_VERSION < 7
 # error These bindings need PHP 7 or later - to generate PHP5 bindings use: SWIG < 4.0.0 and swig -php5
 #endif
 
-#include "ext/standard/php_string.h"
+#include "zend_exceptions.h"
+
 #include <stdlib.h> /* for abort(), used in generated code. */
 
 #define SWIG_BOOL_CONSTANT(N, V) REGISTER_BOOL_CONSTANT(#N, V, CONST_CS | CONST_PERSISTENT)