Fixes type definition of StackFrame

Summary:
**Motivation**
This PR fixes the flow type definition of StackFrame in parseErrorStack.js. The methodName was missing and the column could be `null`. We integrate with it in our codebase and we wanted to use `methodName`, but flow complained.

Refer to this file for possible values: [github.com/errwischt/stacktrace-parser/blob/master/lib/stacktrace-parser.js](https://github.com/errwischt/stacktrace-parser/blob/master/lib/stacktrace-parser.js)

This also allowed me to remove a flow error suppression.

**Test plan (required)**
I ran flow on the project, no errors
Closes https://github.com/facebook/react-native/pull/12499

Differential Revision: D4619885

Pulled By: ericvicenti

fbshipit-source-id: 0bf5a2304cb0dc9f2c6df026a5cee71c8a419c01

Libraries/Core/Devtools/parseErrorStack.js

@@ -12,9 +12,10 @@
 'use strict';
 
 export type StackFrame = {
+  column: ?number,
   file: string,
   lineNumber: number,
-  column: number,
+  methodName: string,
 };
 
 var stacktraceParser = require('stacktrace-parser');

Libraries/Core/Timers/JSTimers.js

@@ -40,8 +40,6 @@ function _allocateCallback(func: Function, type: JSTimerType): number {
     e.framesToPop = 1;
     const stack = parseErrorStack(e);
     if (stack) {
-      /* $FlowFixMe(>=0.32.0) - this seems to be putting something of the wrong
-       * type into identifiers */
       JSTimersExecution.identifiers[freeIndex] = stack.shift();
     }
   }