Revert "Build iOS unittest target in unopt builds"

[cyanglaz]

Reverts #44301

Traceback (most recent call last):
  File "/Volumes/Work/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 1286, in <module>
    sys.exit(main())
  File "/Volumes/Work/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 1269, in main
    run_objc_tests(args.ios_variant, args.objc_filter)
  File "/Volumes/Work/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 721, in run_objc_tests
    ensure_ios_tests_are_built(ios_out_dir)
  File "/Volumes/Work/s/w/ir/cache/builder/src/flutter/testing/run_tests.py", line 625, in ensure_ios_tests_are_built
    assert flutter_dylib_time <= ios_test_lib_time, final_message
AssertionError: /Volumes/Work/s/w/ir/cache/builder/src/out/ios_debug_sim_arm64_extension_safe/libios_test_flutter.dylib is older than /Volumes/Work/s/w/ir/cache/builder/src/out/ios_debug_sim_arm64_extension_safe/libFlutter.dylib. Please run the following commands: 
gn --ios --unoptimized --runtime-mode=debug --no-lto --simulator
ninja -C /Volumes/Work/s/w/ir/cache/builder/src/out/ios_debug_sim_arm64_extension_safe ios_test_flutter

It failed we in run_test.py we check if the ios_test is built after the framework, which is not true anymore after moving the test inside the build target.

[cyanglaz]

Landing on red to fix the tree.