[libc++][test] Remove disable_missing_braces_warning.h from tests

Several tests include `disable_missing_braces_warning.h` but do not need
to. Remove the include.

Inspired from discussion at https://reviews.llvm.org/D109668

Reviewed By: ldionne, #libc, Mordante

Differential Revision: https://reviews.llvm.org/D109711

libcxx/test/std/containers/sequences/array/array.data/data.pass.cpp

@@ -16,10 +16,6 @@
 
 #include "test_macros.h"
 
-// std::array is explicitly allowed to be initialized with A a = { init-list };.
-// Disable the missing braces warning for this reason.
-#include "disable_missing_braces_warning.h"
-
 struct NoDefault {
     TEST_CONSTEXPR NoDefault(int) { }
 };