build: remove dynamic-pthread-stacks patch

[cfriedt]

Once zephyrproject-rtos/zephyr#29029 is merged, we can remove zephyr-dynamic-pthread-stacks.patch from the build process. This ticket is here to track the upstream ticket and ensure it gets merged eventually.

The README.rst file should be updated to reflect the patches that must be applied.

[cfriedt]

The upstream fix also depends on zephyrproject-rtos/zephyr#26999 where the goal is to create a k_alloc_thread_stack() system call. With that system call in place, the pthread change is trivial.

cfriedt/issue/26999/add-a-stack-allocation-api aims to fix zephyrproject-rtos/zephyr#26999 but is currently WIP.

[cfriedt]

Once zephyrproject-rtos/zephyr#29029 is merged, we can remove zephyr-dynamic-pthread-stacks.patch from the build process. This ticket is here to track the upstream ticket and ensure it gets merged eventually.

That PR has been moved to zephyrproject-rtos/zephyr#31603 and is currently WIP