don't pin build number of libtorch in pytorch (for non-megabuild)

otherwise conda breaks
```
conda_build.exceptions.RecipeError: Mismatching hashes in recipe. Exact pins in dependencies that contribute to the hash often cause this. Can you change one or more exact pins to version bound constraints?
Involved packages were:
Mismatching package: libtorch (id cpu_generic_habf3c96_0); dep: libtorch 2.6.0.rc7 *0; consumer package: pytorch
```

Author: h-vetinari

recipe/meta.yaml

@@ -292,8 +292,9 @@ outputs:
         - {{ pin_subpackage('libtorch', exact=True) }}
       run:
         - {{ pin_subpackage('libtorch', exact=True) }}  # [megabuild]
-        # for non-megabuild, allow libtorch from any python version
-        - libtorch {{ version }}.* *_{{ build }}        # [not megabuild]
+        # for non-megabuild, allow libtorch from any python version;
+        # pinning build number would be nice but breaks conda
+        - libtorch {{ version }}.*                      # [not megabuild]
         - llvm-openmp    # [osx]
         - intel-openmp {{ mkl }}  # [win]
         - libblas * *{{ blas_impl }}  # [blas_impl == "mkl"]