Remove unused monomorphization code. (#5266)

## Description

This removes monomorphization code that was added previously by Emily,
but never got finished and is thus unused currently.

## Checklist

- [ ] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [ ] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

sway-core/src/decl_engine/template.rs

@@ -20,6 +20,7 @@ where
         Template(value)
     }
 
+    #[allow(dead_code)]
     pub(crate) fn inner(&self) -> &T {
         &self.0
     }

sway-core/src/lib.rs

@@ -15,7 +15,6 @@ pub mod decl_engine;
 pub mod ir_generation;
 pub mod language;
 mod metadata;
-mod monomorphize;
 pub mod query_engine;
 pub mod semantic_analysis;
 pub mod source_map;