Bug 1505573 - [Mac] Enable sandbox early startup by default on all releases (ride the trains) r=Alex_Gaynor

Let sandbox early startup ride the trains by setting security.sandbox.content.mac.earlyinit=true on all releases, not just Nightly.

Differential Revision: https://phabricator.services.mozilla.com/D13470

--HG--
extra : moz-landing-system : lando

browser/app/profile/firefox.js

@@ -1028,7 +1028,7 @@ pref("security.sandbox.gpu.level", 0);
 pref("security.sandbox.gmp.win32k-disable", false);
 #endif
 
-#if defined(NIGHTLY_BUILD) && defined(XP_MACOSX) && defined(MOZ_SANDBOX)
+#if defined(XP_MACOSX) && defined(MOZ_SANDBOX)
 // Start the Mac sandbox early during child process startup instead
 // of when messaged by the parent after the message loop is running.
 pref("security.sandbox.content.mac.earlyinit", true);