[TF-M] Branch release/1.7.x to be deleted

Hi,

I plan to delete the branch release/1.7.x at the end of this week (after May 26) following TF-M release processhttps://tf-m-user-guide.trustedfirmware.org/releases/release_process.html#release-cadence-and-process. Please let me know if someone is dependent on it and needs more time to detach from it.

Thanks, Anton