Disable fdtrack post-fork.

Also delete some fdsan code that attempts to check for the post-fork
state, but never will, because we update the cached pid upon fork.

Bug: http://b/174542867
Test: /data/nativetest64/bionic-unit-tests/bionic-unit-tests
Test: treehugger
Change-Id: I9b748dac9de9b4c741897d93e64d31737e52bf8e
diff --git a/libfdtrack/fdtrack.cpp b/libfdtrack/fdtrack.cpp
index fd56274..2e9cfbc 100644
--- a/libfdtrack/fdtrack.cpp
+++ b/libfdtrack/fdtrack.cpp
@@ -93,6 +93,8 @@
     android_fdtrack_hook_t expected = nullptr;
     installed = android_fdtrack_compare_exchange_hook(&expected, &fd_hook);
   }
+
+  android_fdtrack_set_globally_enabled(true);
 }
 
 __attribute__((destructor)) static void dtor() {