perfetto-ui: Remove the special mechanism for local files

ControllerProxy currently has three methods:
- initAndGetState
- dispatch
- addLocalFile

Removing addLocalFile will allow us to remove ControllerProxy from
globals and sets the stage for removing initAndGetState and hence
ControllerProxy as a whole.

Change-Id: I56a0f0aeab880f2fb5c67108a4a702fa06887d97
diff --git a/ui/src/common/state.ts b/ui/src/common/state.ts
index 6e9eb7e..89c10cb 100644
--- a/ui/src/common/state.ts
+++ b/ui/src/common/state.ts
@@ -31,7 +31,7 @@
 
 export interface EngineConfig {
   id: string;
-  url: string;
+  source: string|File;
 }
 
 export interface QueryConfig {