tools/addlatexhash.dart: Remove unused import
tools/addlatexhash.dart: Remove unused import

... as reported by the 2-dev.19 analyzer:

```nocode
info: Unused import. (unused_import at [tools] addlatexhash.dart:28)
```

cc @kwalrath

Closes #31958
https://github.com/dart-lang/sdk/pull/31958

GitOrigin-RevId: b4b7f9ab8cd3b04618f29d5ada5eefb1e0592f19
Change-Id: I17195312c8580b9f51d0f00099c6283bf23cdffe
Reviewed-on: https://dart-review.googlesource.com/45620
Reviewed-by: Erik Ernst <251bb01623bfda2cd9151e339a6e783ca432874c@google.com>
Commit-Queue: Erik Ernst <251bb01623bfda2cd9151e339a6e783ca432874c@google.com>

dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk