tests: Remove posix arch_exclude for libcxx

Remove arch_exclude: posix also for
tests/application_development/libcxx.

Signed-off-by: Andrei Emeltchenko <[email protected]>

Author: finikorg

tests/application_development/libcxx/testcase.yaml

@@ -1,11 +1,9 @@
 tests:
   application_development.cpp.libcxx:
-    arch_exclude: posix
     platform_exclude: qemu_x86_coverage
     min_flash: 54
     tags: cpp
   application_development.cpp.libcxx.exceptions:
-    arch_exclude: posix
     platform_exclude: qemu_x86_coverage
     min_flash: 54
     tags: cpp