Remove MetricDefinition lookup via tuning job in TrainingJobAnalytics

[apacker]

Issue #, if available:
N/A

Description of changes:
Remove MetricDefinition lookup via tuning job in TrainingJobAnalytics. MetricDefinition is now available on all built-in algorithms.

Merge Checklist

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• I have added tests that prove my fix is effective or that my feature works (if appropriate)
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[mvsusp]

Tox and Pylint failed because an unused method, fix the method and ask for another review.

TOTAL                                                                               4323    269    94%
flake8 create: /home/travis/build/aws/sagemaker-python-sdk/.tox/flake8
flake8 installdeps: flake8, flake8-future-import
flake8 inst: /home/travis/build/aws/sagemaker-python-sdk/.tox/.tmp/package/1/sagemaker-1.14.2.zip
flake8 installed: boto3==1.9.45,botocore==1.12.45,cached-property==1.5.1,certifi==2018.10.15,chardet==3.0.4,docker==3.5.1,docker-compose==1.23.1,docker-pycreds==0.3.0,dockerpty==0.4.1,docopt==0.6.2,docutils==0.14,flake8==3.6.0,flake8-future-import==0.4.5,idna==2.7,jmespath==0.9.3,jsonschema==2.6.0,mccabe==0.6.1,numpy==1.15.4,protobuf==3.6.1,protobuf3-to-dict==0.1.5,pycodestyle==2.4.0,pyflakes==2.0.0,python-dateutil==2.7.5,PyYAML==3.13,requests==2.20.1,s3transfer==0.1.13,sagemaker==1.14.2,scipy==1.1.0,six==1.11.0,texttable==0.9.1,urllib3==1.24.1,websocket-client==0.54.0
flake8 run-test-pre: PYTHONHASHSEED='1088988466'
flake8 runtests: commands[0] | flake8
./src/sagemaker/analytics.py:23:1: F401 'sagemaker.utils.extract_name_from_job_arn' imported but unused
ERROR: InvocationError for command '/home/travis/build/aws/sagemaker-python-sdk/.tox/flake8/bin/flake8' (exited with code 1)
pylint create: /home/travis/build/aws/sagemaker-python-sdk/.tox/pylint
pylint installdeps: pylint>=2.1
pylint inst: /home/travis/build/aws/sagemaker-python-sdk/.tox/.tmp/package/1/sagemaker-1.14.2.zip
pylint installed: astroid==2.0.4,boto3==1.9.45,botocore==1.12.45,cached-property==1.5.1,certifi==2018.10.15,chardet==3.0.4,docker==3.5.1,docker-compose==1.23.1,docker-pycreds==0.3.0,dockerpty==0.4.1,docopt==0.6.2,docutils==0.14,idna==2.7,isort==4.3.4,jmespath==0.9.3,jsonschema==2.6.0,lazy-object-proxy==1.3.1,mccabe==0.6.1,numpy==1.15.4,protobuf==3.6.1,protobuf3-to-dict==0.1.5,pylint==2.1.1,python-dateutil==2.7.5,PyYAML==3.13,requests==2.20.1,s3transfer==0.1.13,sagemaker==1.14.2,scipy==1.1.0,six==1.11.0,texttable==0.9.1,typed-ast==1.1.0,urllib3==1.24.1,websocket-client==0.54.0,wrapt==1.10.11
pylint run-test-pre: PYTHONHASHSEED='1088988466'
pylint runtests: commands[0] | python -m pylint --rcfile=.pylintrc src/sagemaker
************* Module sagemaker.analytics
src/sagemaker/analytics.py:23:0: W0611: Unused extract_name_from_job_arn imported from sagemaker.utils (unused-import)
------------------------------------
Your code has been rated at 10.00/10
ERROR: InvocationError for command '/home/travis/build/aws/sagemaker-python-sdk/.tox/pylint/bin/python -m pylint --rcfile=.pylintrc src/sagemaker' (exited with code 4)
___________________________________ summary ____________________________________
  py35: commands succeeded
ERROR:   flake8: commands failed
ERROR:   pylint: commands failed
The command "tox tests/unit" exited with 1.