librustc: Remove the &LIFETIME EXPR production from the language.

This was parsed by the parser but completely ignored; not even stored in
the AST!

This breaks code that looks like:

    static X: &'static [u8] = &'static [1, 2, 3];

Change this code to the shorter:

    static X: &'static [u8] = &[1, 2, 3];

Closes #15312.

[breaking-change]

src/libsyntax/parse/parser.rs

@@ -2400,7 +2400,6 @@ impl<'a> Parser<'a> {
           }
           token::BINOP(token::AND) | token::ANDAND => {
             self.expect_and();
-            let _lt = self.parse_opt_lifetime();
             let m = self.parse_mutability();
             let e = self.parse_prefix_expr();
             hi = e.span.hi;