Remove the Paged memory initialization variant (#4046)

* Remove the `Paged` memory initialization variant

This commit simplifies the `MemoryInitialization` enum by removing the
`Paged` variant. The `Paged` variant was originally added for uffd, but
that support has now been removed in #4040. This is no longer necessary
but is still used as an intermediate step of becoming a `Static` variant
of initialized memory (which copy-on-write uses). As a result this
commit largely modifies the static initialization of memory steps and
folds the two methods together.

* Apply suggestions from code review

Co-authored-by: Peter Huene <peter@huene.dev>

Co-authored-by: Peter Huene <peter@huene.dev>

crates/runtime/src/instance/allocator.rs

@@ -396,7 +396,7 @@ fn check_init_bounds(instance: &mut Instance, module: &Module) -> Result<(), Ins
             check_memory_init_bounds(instance, initializers)?;
         }
         // Statically validated already to have everything in-bounds.
-        MemoryInitialization::Paged { .. } | MemoryInitialization::Static { .. } => {}
+        MemoryInitialization::Static { .. } => {}
     }
 
     Ok(())