Cleanup some trivial TODOs.

1) "fix the system properties design" is written for the old protocol,
   so we've already changed the design.  There are no other further
   planned changes.
2) "don't drag in all the macros, just the types." is not likely to
   happen or be particularly impactful.
3) "Find a location suitable for these functions ..." is refering to
   legacy code.  More likely that this code will be removed before we
   find a serious reason to fix this TODO.
4) "(73062966) We still don't have a good way ..." is stale; we fixed
   this bug and added the appropriate mechanism.

Test: n/a
Change-Id: I23991692cdeb81ad00844a6a1680900ff384208b
diff --git a/libc/include/bits/stdatomic.h b/libc/include/bits/stdatomic.h
index 633cb86..2ce6ee6 100644
--- a/libc/include/bits/stdatomic.h
+++ b/libc/include/bits/stdatomic.h
@@ -41,7 +41,7 @@
  */
 
 #include <stddef.h>  /* For ptrdiff_t. */
-#include <stdint.h>  /* TODO: don't drag in all the macros, just the types. */
+#include <stdint.h>
 // Include uchar.h only when available.  Bionic's stdatomic.h is also used for
 // the host (via a copy in prebuilts/clang) and uchar.h is not available in the
 // glibc used for the host.