Remove on-heap managed memory

As mentioned in this discussion thread, we want to make managed memory always off-heap.

This task include changes:

• Remove `MEMORY_OFF_HEAP`, `MANAGED_MEMORY_OFFHEAP_FRACTION` and `MANAGED_MEMORY_OFFHEAP_SIZE` from `TaskManagerOptions`.
• Remove `onHeapManagedMemory` from `ResourceProfile`, `ResourceSpec` and `TaskExecutorResourceSpec`.
• Remove on heap managed memory from `MemoryManager`
• Remove on heap managed memory fraction from `StreamConfig`.