Remove macOS 10.12 path from ipcz

Chromium requires at least macOS 10.13. This removes code that
handles earlier OS versions.

Bug: none
Change-Id: Ic5c88fad95d245ada0cf9a3bcf2ac4fc684d6d7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4058852
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Ken Rockot <rockot@google.com>
Auto-Submit: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1076289}
NOKEYCHECK=True
GitOrigin-RevId: f9e993585d5c688b8ae3133c225c3c1caef32061
diff --git a/src/reference_drivers/random.cc b/src/reference_drivers/random.cc
index 83c0e6f..e228466 100644
--- a/src/reference_drivers/random.cc
+++ b/src/reference_drivers/random.cc
@@ -45,7 +45,7 @@
 
 namespace {
 
-#if defined(OS_POSIX)
+#if defined(OS_POSIX) && !BUILDFLAG(IS_MAC)
 void RandomBytesFromDevUrandom(absl::Span<uint8_t> destination) {
   static int urandom_fd = [] {
     for (;;) {
@@ -92,12 +92,8 @@
     }
   }
 #elif BUILDFLAG(IS_MAC)
-  if (__builtin_available(macOS 10.12, *)) {
-    const bool ok = getentropy(destination.data(), destination.size()) == 0;
-    ABSL_ASSERT(ok);
-  } else {
-    RandomBytesFromDevUrandom(destination);
-  }
+  const bool ok = getentropy(destination.data(), destination.size()) == 0;
+  ABSL_ASSERT(ok);
 #elif BUILDFLAG(IS_IOS)
   RandomBytesFromDevUrandom(destination);
 #elif BUILDFLAG(IS_NACL)