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/Cargo.toml

@@ -28,9 +28,6 @@ epi = { version = "0.14.0", path = "../epi" }
 glium = "0.30"
 webbrowser = "0.5"
 
-# feature "http":
-ureq = { version = "2.0", optional = true }
-
 # feature "persistence":
 directories-next = { version = "2", optional = true }
 ron = { version = "0.6", optional = true }
@@ -48,7 +45,6 @@ default = ["default_fonts"]
 # If set, egui will use `include_bytes!` to bundle some fonts.
 # If you plan on specifying your own fonts you may disable this feature.
 default_fonts = ["egui/default_fonts"]
-http = ["epi/http", "ureq"]
 persistence = [
     "directories-next",
     "egui/persistence",