chore: Remove unused require statements as picked up by the Elixir 1.20.0-rc.1 compiler

[sevenseacat]

There's still one type warning in assert_has_issue:

     warning: unknown key .issues in expression:

         igniter.issues

     the given type does not have the given key:

         dynamic(%Rewrite{
           sources: term(),
           extensions: term(),
           hooks: term(),
           dot_formatter: term(),
           excluded: term()
         })

     where "igniter" was given the type:

         # type: dynamic(%Rewrite{})
         # from: lib/igniter/test.ex:427:24
         Rewrite.source(igniter, path)

     typing violation found at:
     │
 435 │       if !Enum.any?(igniter.issues, fn found_issue ->
     │                             ~~~~~~
     │
     └─ (igniter 0.7.0) lib/igniter/test.ex:435:29: Igniter.Test.assert_has_issue/3

But I thought I'd fix the low-hanging fruit. :)

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