Replace all http code in epi/eframe/egui_glium/egui_web with ehttp (#697)

I've extracted all the http request code and turned it
into its own crate at <https://github.com/emilk/ehttp>.

There was never a reason for the HTTP request library to be part of
`eframe`. Much better to have it as its own crate!

egui_glium/src/lib.rs

@@ -19,8 +19,6 @@
 #![allow(clippy::manual_range_contains, clippy::single_match)]
 
 mod backend;
-#[cfg(feature = "http")]
-pub mod http;
 mod painter;
 #[cfg(feature = "persistence")]
 pub mod persistence;