boards: st: remove the pre_dt_board wihout with ospi node

Since the ospi@ node does not exist anymore for the stm32u5 device
there is no more need for this pre_dt_board.cmake file.

(cherry picked from commit 8a305df)

Original-Signed-off-by: Francois Ramu <[email protected]>
GitOrigin-RevId: 8a305df
Cr-Build-Id: 8725452993329915921
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8725452993329915921
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: I48746877bb0369e7d891c74f718b6b3b424bef92
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/6183337
Commit-Queue: Jonathon Murphy <[email protected]>
Tested-by: ChromeOS Prod (Robot) <[email protected]>
Reviewed-by: Jonathon Murphy <[email protected]>

Author: Francois Ramu