ci: remove dependency on pull/43987/head to track zephyr main directly

[cfriedt]

Is your enhancement proposal related to a problem? Please describe.
Currently, in west.yml, we are tracking zephyrproject-rtos/zephyr#43987 rather than HEAD in the zephyr repository.

In the interest of reducing the number of moving parts for integration, I think it would make sense to simply track HEAD in the zephyr repository.

However, that comes at the cost of reintroducing dozens (hundreds?) of changes back into the Thrift fork of the form

#ifdef __ZEPHYR__
#include <zephyr/posix/unistd.h>
#else
#include <unistd.h>
#endif

Describe the solution you'd like
The nice thing about doing the above, is that we can simply use and benefit from zephyrproject-rtos/zephyr#43987 when it is eventually merged upstream. Additionally, since zephyrproject-rtos/zephyr#43987 still needs work to separate it into separate commits, and since there are likely some architectural mistakes that need to be changed upstream, and furthermore, since all of this is "evening and weekend work" as it has not been prioritized by my employer, it could be a while until all of it is finished.

At least the .upstream Thrift changes can be pinned to v0.16.0 and can be relatively self-contained.

Describe alternatives you've considered
Making gsoc-2022-thrift depend on long-lived changes in branch is not a great idea.

Additional context