Remove unused import from transformer.py

Removed unused import of mr_ from numpy.ma

Author: sogolsahebi

src/imgtools/transforms/transformer.py

@@ -2,7 +2,6 @@
 from typing import Generic, Sequence, TypeVar
 
 import SimpleITK as sitk
-from numpy.ma import mr_
 
 from imgtools.coretypes.base_masks import VectorMask
 from imgtools.coretypes.base_medimage import MedImage
@@ -169,4 +168,4 @@ def main() -> None:
 
 
 if __name__ == "__main__":
-    main()
+    main()