Use Hermes Engine from CocoaPods and fix Circle CI (#33478)

Summary:
Undoing the recent change that enabled Hermes to be built from source by default.
Building Hermes from source now requires the use of the  BUILD_HERMES_SOURCE envvar, again.

To be re-enabled shortly.

Pull Request resolved: #33478

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D35100459

fbshipit-source-id: ec83fcdf2432c689b0c02f86fbabcc8625975d51

scripts/react_native_pods.rb

@@ -110,8 +110,12 @@ def use_react_native! (options={})
 
   if hermes_enabled
     pod 'React-hermes', :path => "#{prefix}/ReactCommon/hermes"
-    hermes_source_path = downloadAndConfigureHermesSource(prefix)
-    pod 'hermes-engine', :path => "#{hermes_source_path}/hermes-engine.podspec"
+    if ENV['BUILD_HERMES_SOURCE'] == '1'
+      hermes_source_path = downloadAndConfigureHermesSource(prefix)
+      pod 'hermes-engine', :path => "#{hermes_source_path}/hermes-engine.podspec"
+    else
+      pod 'hermes-engine', '~> 0.11.0'
+    end
     pod 'libevent', '~> 2.1.12'
   end