[libc++] Remove <stdbool.h> (#164595)

`<stdbool.h>` is provided by the compiler and both Clang and GCC provide
C++-aware versions of these headers, making our own wrapper header
entirely unnecessary.

Author: philnik777

libcxx/include/CMakeLists.txt

@@ -1066,7 +1066,6 @@ set(files
   sstream
   stack
   stdatomic.h
-  stdbool.h
   stddef.h
   stdexcept
   stdio.h

libcxx/include/module.modulemap.in

@@ -2437,10 +2437,6 @@ module std_stdatomic_h [system] {
   header "stdatomic.h"
   export *
 }
-module std_stdbool_h [system] {
-  // <stdbool.h>'s __bool_true_false_are_defined macro requires textual inclusion.
-  textual header "stdbool.h"
-}
 module std_stddef_h [system] {
   // <stddef.h> supports being included multiple times with different pre-defined macros
   textual header "stddef.h"