cmake: remove obsolete CONFIG_ZTEST_NEW_API from CMakeLists.txt

With the introduction of Kconfig for unit_testing board and setting
ZTEST_NEW_API in testcase.yaml, the need and support of setting this
directly in CMakeLists.txt is obsolete.

Remove the code line.

(cherry picked from commit abc3be5)

Original-Follow-up: #49243, #48732
Original-Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
GitOrigin-RevId: abc3be5
Change-Id: I519cbe12526ac75e6aeb294745b55c30e5e3d3e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/3882560
Tested-by: CopyBot Service Account <copybot.service@gmail.com>
Commit-Queue: Aaron Massey <aaronmassey@google.com>
Tested-by: Aaron Massey <aaronmassey@google.com>
Reviewed-by: Aaron Massey <aaronmassey@google.com>

tests/bluetooth/controller/ctrl_cte_req/CMakeLists.txt

@@ -9,7 +9,6 @@ FILE(GLOB SOURCES
   src/*.c
 )
 
-set(CONFIG_ZTEST_NEW_API y)
 project(bluetooth_ull_llcp_le_cte_req)
 find_package(Zephyr COMPONENTS unittest HINTS $ENV{ZEPHYR_BASE})
 include(${ZEPHYR_BASE}/tests/bluetooth/controller/common/defaults_cmake.txt)