Remove duplicate tests

Remove duplicate test (iterator_018.phpt)

This is exactly the same as iterator_011.phpt.

Remove duplicate test (offsets_chaining_2.phpt)

This is exactly the same as offsets_chaining_1.phpt.

Remove duplicate test (offsets_chaining_4.phpt)

This is exactly the same as offsets_chaining_3.phpt.

Remove duplicate test (ReflectionObject_export_basic1.phpt)

This is exactly the same as ReflectionObject___toString_basic1.phpt.

Remove duplicate test (ReflectionObject_export_basic2.phpt)

This is exactly the same as ReflectionObject___toString_basic2.phpt.

Closes phpGH-5467.

Author: alexdowad