<generator>: Don't use operator new[] and operator delete[]

[JMazurkiewicz]

_Promise_allocator<void>'s operator new(size_t) is specified to allocate memory with allocator<_Aligned_block> (see [coro.generator.promise]/17), which internally uses ::operator new, not ::operator new[] (see [allocator.members]/5).

[StephanTLavavej]

Great catch! 😺 I adjusted the PR title due to a mega-nitpick - operator new[] is the function being avoided here, whereas the new operator is when new T appears in source code. (new T[n] isn't really using a new[] operator, although it can generally be thought of that way.)