[cleanup] Replace PFX with %p in DR-printed format strings

In PR #3860 I made this key change:

+ Changes the "PFX" format string macro from %x-based to %p-based, in order
  to support enabling format string warnings.  This is now possible because
  on Windows we use our own printing code, rather than the ntdll code,
  making the %p style consistent across platforms.
  We do *not* make this change for native test apps, to avoid breaking
  the golden output.

%p is more convenient than "PFX" because it's so much shorter without having to unquote and requote. As noted, native test apps and other native code using system library print routines shouldn't use %p: but client and core code can. This is a proposed cleanup to go and change the existing code to use %p. It would be a lot of code churn in the history. Another downside is that if we then share code or model native code on %p-using DR/client code we'll have platform inconsistencies.