Clean up adc.py

[DanielSank]

• Line lengths
• Dangling white space
• Remove copypasta from ADC interface spec sheet

[jwenner]

FYI, there's an fpga test which this breaks:

  test_fpga_server.top_level_collect 
('fpgalib/test/test_fpga_server.py', None, 'fpgalib/test/test_fpga_server.py')
.venv/local/lib/python2.7/site-packages/_pytest/python.py:610: in _importtestmodule
    mod = self.fspath.pyimport(ensuresyspath=importmode)
.venv/local/lib/python2.7/site-packages/py/_path/local.py:650: in pyimport
    __import__(modname)
.venv/local/lib/python2.7/site-packages/_pytest/assertion/rewrite.py:171: in load_module
    py.builtin.exec_(co, mod.__dict__)
servers/fpgalib/test/test_fpga_server.py:28: in <module>
    import ghz_fpga_server
servers/ghz_fpga_server.py:212: in <module>
    import fpgalib.adc as adc
E     File "/opt/TeamCity/buildAgent/work/872fe26a728e05ba/servers/fpgalib/adc.py", line 60
E       self.boardGroup = group
E          ^
E   SyntaxError: invalid syntax

[maffoo]

Python 2.7 has dict comprehensions so you could do

channels = {i: info[i]
            for i in range(self.DEMOD_CHANNELS) if i in info}

[maffoo]

A few small comments, and need to fix syntax error; otherwise LGTM.