Fixes two elided_named_lifetimes warnings

[smoelius]

When I build Solang, I see these two warnings:

warning: elided lifetime has a name
   --> src/emit/mod.rs:375:18
    |
369 |     pub fn binary<'a>(
    |                   -- lifetime `'a` declared here
...
375 |     ) -> binary::Binary {
    |                  ^^^^^^ this elided lifetime gets resolved as `'a`
    |
    = note: `#[warn(elided_named_lifetimes)]` on by default

warning: elided lifetime has a name
   --> src/sema/builtin_structs.rs:243:59
    |
243 |     pub fn definition<'a>(&'a self, ns: &'a Namespace) -> &StructDecl {
    |                       -- lifetime `'a` declared here      ^ this elided lifetime gets resolved as `'a`

This PR addresses both of the warnings.