Unpin oauth2client after 1.4.4 release.

oauth2client-1.4.4 fixes the bug we were pinning to avoid:

    $ tox --recreate -e regression
    GLOB sdist-make: /home/tseaver/projects/agendaless/Google/src/gcloud-python/setup.py
    regression recreate: /home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/regression
    regression installdeps: unittest2
    regression inst: /home/tseaver/projects/agendaless/Google/src/gcloud-python/.tox/dist/gcloud-0.3.0.zip
    regression runtests: PYTHONHASHSEED='1425230368'
    regression runtests: commands[0] | /home/tseaver/projects/agendaless/Google/src/gcloud-python/scripts/run_regression.sh

    # If we're on Travis, we need to set up the environment.
    if [[ "${TRAVIS}" == "true" ]]; then
    # If merging to master and not a pull request, run regression test.
    if [[ "${TRAVIS_BRANCH}" == "master" ]] && \
            [[ "${TRAVIS_PULL_REQUEST}" == "false" ]]; then
        echo "Running in Travis during merge, decrypting stored key file."

        # Convert encrypted key file into decrypted file to be used.
        openssl aes-256-cbc -K $encrypted_a1b222e8c14d_key \
            -iv $encrypted_a1b222e8c14d_iv \
            -in regression/key.p12.enc \
            -out $GCLOUD_TESTS_KEY_FILE -d
    else
        echo "Running in Travis during non-merge to master, doing nothing."
        exit
    fi
    fi

    # Run the regression tests for each tested package.
    python regression/run_regression.py --package datastore
    test_allocate_ids (datastore.TestDatastoreAllocateIDs) ... ok
    test_ancestor_query (datastore.TestDatastoreQuery) ... ok
    test_limit_queries (datastore.TestDatastoreQuery) ... ok
    test_ordered_query (datastore.TestDatastoreQuery) ... ok
    test_projection_query (datastore.TestDatastoreQuery) ... ok
    test_query___key___filter (datastore.TestDatastoreQuery) ... ok
    test_query_group_by (datastore.TestDatastoreQuery) ... ok
    test_query_multiple_filters (datastore.TestDatastoreQuery) ... ok
    test_query_paginate_with_offset (datastore.TestDatastoreQuery) ... ok
    test_query_paginate_with_start_cursor (datastore.TestDatastoreQuery) ... ok
    test_query_simple_filter (datastore.TestDatastoreQuery) ... ok
    test_empty_kind (datastore.TestDatastoreSave) ... ok
    test_post_with_generated_id (datastore.TestDatastoreSave) ... ok
    test_post_with_id (datastore.TestDatastoreSave) ... ok
    test_post_with_name (datastore.TestDatastoreSave) ... ok
    test_save_multiple (datastore.TestDatastoreSave) ... ok
    test_save_key_self_reference (datastore.TestDatastoreSaveKeys) ... ok
    test_transaction (datastore.TestDatastoreTransaction) ... ok

    ----------------------------------------------------------------------
    Ran 18 tests in 9.684s

    OK
    python regression/run_regression.py --package storage
    test_create_bucket (storage.TestStorageBuckets) ... ok
    test_get_buckets (storage.TestStorageBuckets) ... ok
    test_list_files (storage.TestStorageListFiles) ... ok
    test_paginate_files (storage.TestStorageListFiles) ... ok
    test_first_level (storage.TestStoragePseudoHierarchy) ... ok
    test_root_level_w_delimiter (storage.TestStoragePseudoHierarchy) ... ok
    test_second_level (storage.TestStoragePseudoHierarchy) ... ok
    test_third_level (storage.TestStoragePseudoHierarchy) ... ok
    test_create_signed_delete_url (storage.TestStorageSignURLs) ... ok
    test_create_signed_read_url (storage.TestStorageSignURLs) ... ok
    test_copy_existing_file (storage.TestStorageWriteFiles) ... ok
    test_direct_write_and_read_into_file (storage.TestStorageWriteFiles) ... ok
    test_large_file_write_from_stream (storage.TestStorageWriteFiles) ... ok
    test_small_file_write_from_filename (storage.TestStorageWriteFiles) ... ok
    test_write_metadata (storage.TestStorageWriteFiles) ... ok

    ----------------------------------------------------------------------
    Ran 15 tests in 24.126s

    OK
    ___________________________________ summary ____________________________________
    regression: commands succeeded
    congratulations :)
    $ ls -l  .tox/regression/lib/python2.7/site-packages/ | grep oauth2client
    drwxrwxr-x  2 tseaver tseaver   4096 Dec 15 12:15 oauth2client
    drwxrwxr-x  2 tseaver tseaver   4096 Dec 15 12:15 oauth2client-1.4.4-py2.7.egg-info