Convert 3rdparty/python to use the python_requirements target.

[mateor]

Twitter commons was using a wrapper function around its python
dependencies to create python_requirement_library targets.
The python_requirements library is able to understand a pip
requirements.txt file and convert each entry into the
python_requirement_library target needed by Pants.

The python_requirements target uses the project name as a target
name. The original wrapper was maintained for a few dependencies
when their name clashed with Pants BUILD file conventions.

I also removed the easy_install thrift, it looks like it was
put in place to service aurora, who was later unblocked.

Let me know if you think it should be returned:
pantsbuild/pants#2533

The purpose of this change is to enable a simple interface to convert
some python dependencies from being hardcoded to a single rev into
being able to be satisfied by a release range. I will submit
any dependency version changes separately.

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[grimreaper]

Thank you for your contribution. Unfortunately, we’re not going to continue maintaining twitter-commons and are archiving all pull requests.