feat(all): remove X-Requested-With header from HTTP requests

[m1ga]

Removing "twitter workaround" from the SDK that and removed fixed X-Requested-With header.
If needed user can still add it but having it as a default causes more errors.

Old info for Twitter: https://jira-archive.titaniumsdk.com/TIMOB/TIMOB-729

Test
run and check for the returned output

var url = "https://httpbin.org/post";
var client = Ti.Network.createHTTPClient({
	onload: function(e) {
		Ti.API.info(this.responseText);
	}
});
client.open("POST", url);
client.send();

X-Requested-With": "XMLHttpRequest", shouldn't be visible after this PR

Requested in Slack: paySmart3D checks for "ajax requests" and didn't work when the header is there.
Feedback from slack: Removing that line made the API call successful.