Remove trailing whitespace from license text

lib/spack/spack/test/mock_packages/fake.py

lib/spack/spack/test/mock_packages/indirect_mpich.py

lib/spack/spack/test/mock_packages/libdwarf.py

lib/spack/spack/test/mock_packages/libelf.py

lib/spack/spack/test/mock_packages/mpich.py

lib/spack/spack/test/mock_packages/mpich2.py

lib/spack/spack/test/mock_packages/mpileaks.py

lib/spack/spack/test/mock_packages/multimethod.py

lib/spack/spack/test/mock_packages/zmpi.py

lib/spack/spack/test/mock_packages_test.py

lib/spack/spack/test/multimethod.py

lib/spack/spack/test/spec_dag.py

lib/spack/spack/test/spec_semantics.py

lib/spack/spack/test/spec_syntax.py

lib/spack/spack/test/stage.py

lib/spack/spack/test/url_parse.py

lib/spack/spack/test/versions.py

lib/spack/spack/tty.py

lib/spack/spack/url.py

lib/spack/spack/util/__init__.py