Drop all code related to generating CLIs.

All of the generated CLI code depends on google-apputils, which is a
python2.7-only library. Given that no one is directly using the generated CLIs
right now, there's no point in porting it to (say) argparse.

Fixes #8.

The bulk of the change here is just deletion; I suspect there are now more
dangling references, so some tree-shaking/dead-code-elimination could be
fruitful. Other changes:

* the client generation test now ensures each client can be imported, as
  opposed to invoking `<generated_cli> --help`.
* the samples and sample generating script drop the CLIs.

Note that I *did* keep the flag for `gen_client`, so that any existing code
passing `--nogenerate_cli` wouldn't be broken.
diff --git a/setup.py b/setup.py
index c0ab0b8..88ab29a 100644
--- a/setup.py
+++ b/setup.py
@@ -35,12 +35,10 @@
     ]
 
 CLI_PACKAGES = [
-    'google-apputils>=0.4.0',
-    'python-gflags==3.0.6',  # Starting version 3.0.7 py26 is not supported.
+    'python-gflags>=3.0.6',
 ]
 
 TESTING_PACKAGES = [
-    'google-apputils>=0.4.0',
     'unittest2>=0.5.1',
     'mock>=1.0.1',
 ]
@@ -51,9 +49,6 @@
 
 py_version = platform.python_version()
 
-if py_version < '2.7':
-    REQUIRED_PACKAGES.append('argparse>=1.2.1')
-
 _APITOOLS_VERSION = '0.5.22'
 
 with open('README.rst') as fileobj: