Remove 'creating your own error types'

this should end up later in the book, someday

src/SUMMARY.md

@@ -6,7 +6,6 @@
 
 - [Guessing Game Tutorial](ch02-00-guessing-game-tutorial.md)
 
-<<<<<<< a2bc57618340b6257b9a4dd7d4f3993c71cde2e4
 - [Common Programming Concepts in Rust](ch03-00-common-programming-concepts-in-rust.md)
     - [Variable Bindings and Mutability](ch03-01-variable-bindings-and-mutability.md)
     - [Data Types](ch03-02-data-types.md)

src/ch07-03-recoverable-errors-with-result.md

@@ -175,3 +175,6 @@ effects; nothing is returned upon success. Well, functions with no return type,
 as we just saw with `main()`, are the same as returning unit. So we can use
 it as the return type here, too. This leads to the last line of the function,
 the slightly silly-looking `Ok(())`. This is an `Ok()` with a `()` inside.
+
+In chapter XX, we'll learn how to make our own types like these, but for now,
+an understanding of the core `Result<T, E>` is enough.

src/ch07-04-creating-your-own-error-types.md

@@ -1,34 +0,0 @@
-# Creating your own Error types
-
-This pattern of "return an error" is so common, many libraries create their
-own error type, and use it for all of their functions. We can re-write the
-previous example to use `std::io::Result` rathern than a regular `Result`:
-
-```rust
-#![feature(question_mark)]
-
-use std::fs::File;
-use std::io;
-
-fn main() {
-}
-
-pub fn process_file() -> io::Result<()> {
-    let f = File::open("hello.txt")?;
-
-    // do some stuff with f
-
-    Ok(())
-}
-```
-
-`io::Result` looks like this:
-
-```rust
-# use std::io;
-type Result<T> = Result<T, std::io::Error>;
-```
-
-It's a type alias for a regular-old `Result<T, E>`, with the `E` set up to be a
-`std::io::Error`. This means we don't need to worry about the error type in our
-function signatures, which is nice.