Fix pep8 and apply reviewers corrections

The recent python3's refactoring leads us with some pep8 errors which causes CI tests to fail:

  - W293: blank line contains whitespace
  - W291: trailing whitespace
  - F401: imported but unused

Also, in order to keep up to date the reviews, apply most of commented reviews, which are mostly affecting the readability of the source code.

Author: opacam

pythonforandroid/bootstraps/sdl2/__init__.py

@@ -1,7 +1,7 @@
 from pythonforandroid.toolchain import (
     Bootstrap, shprint, current_directory, info, info_main)
 from pythonforandroid.util import ensure_dir
-from os.path import join, exists
+from os.path import join
 import sh
 
 

pythonforandroid/bootstraps/sdl2/build/build.py

@@ -127,8 +127,6 @@ def make_python_zip():
 
     if not exists('private'):
         print('No compiled python is present to zip, skipping.')
-        print('this should only be the case if you are using'
-              'the CrystaX python, python2 or python3')
         return
 
     global python_files

pythonforandroid/recipe.py

@@ -1045,7 +1045,7 @@ class variable.
     '''The configure arguments needed to build the python recipe. Those are
     used in method :meth:`build_arch` (if not overwritten like python3crystax's
     recipe does).
-    
+
     .. note:: This variable should be properly set in subclass.
     '''
 
@@ -1159,12 +1159,10 @@ def prebuild_arch(self, arch):
 
     def include_root(self, arch_name):
         '''The root directory from which to include headers.'''
-        return join(self.get_build_dir(arch_name),
-                    'Include')
+        return join(self.get_build_dir(arch_name), 'Include')
 
     def link_root(self, arch_name):
-        return join(self.get_build_dir(arch_name),
-                    'android-build')
+        return join(self.get_build_dir(arch_name), 'android-build')
 
     @property
     def major_minor_version_string(self):
@@ -1290,7 +1288,7 @@ class TargetHostPythonRecipe(Recipe):
     '''
 
     name = ''
-    '''The hostpython's recipe name. This should be ``hostpython2`` or 
+    '''The hostpython's recipe name. This should be ``hostpython2`` or
     ``hostpython3``
 
     .. warning:: This must be set in inherited class.'''

pythonforandroid/recipes/sdl2/__init__.py

@@ -24,8 +24,7 @@ def get_recipe_env(self, arch=None):
         env['PYTHON_INCLUDE_ROOT'] = self.ctx.python_recipe.include_root(arch.arch)
         env['PYTHON_LINK_ROOT'] = self.ctx.python_recipe.link_root(arch.arch)
 
-        if 'python2' in self.ctx.recipe_build_order or \
-                'python3' in self.ctx.recipe_build_order:
+        if self.ctx.python_recipe.name in ('python2', 'python3'):
             env['EXTRA_LDLIBS'] = ' -lpython{}'.format(
                 self.ctx.python_recipe.major_minor_version_string)
             if 'python3' in self.ctx.recipe_build_order: