deploy-ng: Default platforms to a list of platforms instead of the host platform

The list is:
  * manylinux1_x86_64
  * macosx_10_6_x86_64
  * win_amd64

Of note, win32 is missing from this list. We can add it later if there
is desire.

Also of note, there is now no path to *not* using wheels. We will need
to evaluate if we want to keep this around and, if so, expose it as an
option to users.

direct/src/showutil/dist.py

@@ -206,7 +206,11 @@ class build_apps(setuptools.Command):
         self.exclude_patterns = []
         self.include_modules = {}
         self.exclude_modules = {}
-        self.platforms = []
+        self.platforms = [
+            'manylinux1_x86_64',
+            'macosx_10_6_x86_64',
+            'win_amd64',
+        ]
         self.plugins = []
         self.embed_prc_data = True
         self.extra_prc_files = []
@@ -323,19 +327,10 @@ class build_apps(setuptools.Command):
         self.package_data_dirs = tmp
 
     def run(self):
-        if not self.platforms:
-            platforms = [p3d.PandaSystem.get_platform()]
-            use_wheels = False
-        elif isinstance(self.platforms, basestring):
-            platforms = [self.platforms]
-            use_wheels = True
-        else:
-            platforms = self.platforms
-            use_wheels = True
-        self.announce('Building platforms: {0}'.format(','.join(platforms)), distutils.log.INFO)
+        self.announce('Building platforms: {0}'.format(','.join(self.platforms)), distutils.log.INFO)
 
-        for platform in platforms:
-            self.build_runtimes(platform, use_wheels)
+        for platform in self.platforms:
+            self.build_runtimes(platform, True)
 
     def download_wheels(self, platform):
         """ Downloads wheels for the given platform using pip. This includes panda3d

samples/asteroids/setup.py

@@ -18,12 +18,6 @@ setup(
                 'pandagl',
                 'p3openal_audio',
             ],
-            'platforms': [
-                'manylinux1_x86_64',
-                'macosx_10_6_x86_64',
-                'win32',
-                'win_amd64',
-            ],
         }
     }
 )