Windows: Fix usage of pkgrepo state

`pkgrepo.py` contains this line:

```
from salt.modules.aptpkg import _strip_uri
```

However, `salt.modules.aptpkg` is just not importable on Windows.
Instead of trying to make this module importable on Windows (which
clearly isn't the intent of the module), placed a copy of `_strip_uri`
into `pkgrepo.py` as this is a small function.

Signed-off-by: Sergey Kizunov <sergey.kizunov@ni.com>

salt/states/pkgrepo.py

@@ -92,7 +92,7 @@ import sys
 
 # Import salt libs
 from salt.exceptions import CommandExecutionError, SaltInvocationError
-from salt.modules.aptpkg import _strip_uri
+from salt.ext.six.moves import range  # pylint: disable=import-error,redefined-builtin
 from salt.state import STATE_INTERNAL_KEYWORDS as _STATE_INTERNAL_KEYWORDS
 import salt.utils
 import salt.utils.pkg.deb
@@ -106,6 +106,18 @@ def __virtual__():
     return 'pkg.mod_repo' in __salt__
 
 
+def _strip_uri(repo):
+    '''
+    Remove the trailing slash from the URI in a repo definition
+    '''
+    splits = repo.split()
+    for idx in range(len(splits)):
+        if any(splits[idx].startswith(x)
+               for x in ('http://', 'https://', 'ftp://')):
+            splits[idx] = splits[idx].rstrip('/')
+    return ' '.join(splits)
+
+
 def managed(name, ppa=None, **kwargs):
     '''
     This state manages software package repositories. Currently, :mod:`yum