Rename BridgeProfiling to Systrace for consistency

Summary:
public

Rename the `BridgeProfiling` JS module to `Systrace`, since it's actually just
an API to Systrace markers.

This should make it clearer as we add more perf tooling.

Reviewed By: jspahrsummers

Differential Revision: D2734001

fb-gh-sync-id: 642848fa7340c545067f2a7cf5cef8af1c8a69a2

Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js

@@ -165,8 +165,8 @@ function setUpWebSockets() {
 
 function setUpProfile() {
   if (__DEV__) {
-    var BridgeProfiling = require('BridgeProfiling');
-    BridgeProfiling.swizzleReactPerf();
+    var Systrace = require('Systrace');
+    Systrace.swizzleReactPerf();
   }
 }