pw_build/cmake: Deprecate pw_auto_add_module_tests
pw_build/cmake: Deprecate pw_auto_add_module_tests

Now that it's no longer in use, the pw_auto_add_module_tests
Cmake function is deprecated in favor of direct use of pw_add_test.

Change-Id: I265dc415fce1730dcf5d78918c2257864b32fec5
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/119890
Commit-Queue: Ewout van Bekkum <638f134dbc68778d6b859fb04a64baea2b00b021@google.com>
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Pigweed-Auto-Submit: Ewout van Bekkum <638f134dbc68778d6b859fb04a64baea2b00b021@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed