remove MessageEvent constructors which are impossible to implement

[dirk-thomas]

Removing these constructors from public API since there it is impossible to get the connection header at this point.

@tfoote @wjwwood Please review.

[wjwwood]

I don't understand the context by which they cannot be used, but if that is the case +1, otherwise it should have had a deprecation first.

[dirk-thomas]

The second argument of the internally called init() function are the connection headers. But since the constructor only receives the message and the message does not contain the connection headers anymore the function passes a fake empty map.

[tfoote]

+1

[dirk-thomas]

It looks like that too much external code is relying on these constructors even if they have wrong behavior. So I will revert these changes in order to not break existing code (e84f3e8). Obviously the existing code does not care that the connection header information is just made up.