Also remove all instances of 'self within the codebase.
This fixes #10889.
To make reviewing easier the following files were modified with more than a dumb text replacement:
- `src/test/compile-fail/lifetime-no-keyword.rs`
- `src/test/compile-fail/lifetime-obsoleted-self.rs`
- `src/test/compile-fail/regions-free-region-ordering-incorrect.rs`
- `src/libsyntax/parse/lexer.rs`