Clean up pyflakes warning about imported, but unused modules.

Mostly modules appear to be entirely unused, but some functions take an object
as their first argument and we were using obj->func(...) instead of func(obj,
...) and the former confuses pyflakes.

attic/wscript:1: 'waflib.Utils' imported but unused
ntpfrob/wscript:1: 'waflib.Utils' imported but unused
ntptime/wscript:1: 'waflib.Utils' imported but unused
wafhelpers/configure.py:4: 'waflib.Configure.conf' imported but unused
wafhelpers/configure.py:155: 'wafhelpers.check_type.check_type' imported but unused
wafhelpers/configure.py:156: 'wafhelpers.check_sizeof.check_sizeof' imported but unused
wafhelpers/configure.py:157: 'wafhelpers.check_structfield.check_structfield' imported but unused
wafhelpers/waf.py:2: 'waflib.TaskGen.extension' imported but unused
wafhelpers/waf.py:2: 'waflib.TaskGen.after' imported but unused
wafhelpers/waf.py:2: 'waflib.TaskGen.after_method' imported but unused
wafhelpers/waf.py:2: 'waflib.TaskGen.before' imported but unused