Drop vendoring patch for distro

- python2.6 is no longer supported by pip

```bash
git apply --reverse tasks/vendoring/patches/distro.patch
git rm tasks/vendoring/patches/distro.patch
```

src/pip/_vendor/README.rst

@@ -98,7 +98,6 @@ Modifications
 * ``CacheControl`` has been modified to import its dependencies from ``pip._vendor``
 * ``packaging`` has been modified to import its dependencies from ``pip._vendor``
 * ``requests`` has been modified *not* to optionally load any C dependencies
-* Modified distro to delay importing ``argparse`` to avoid errors on 2.6
 
 
 Automatic Vendoring

src/pip/_vendor/distro.py

@@ -34,6 +34,7 @@ import sys
 import json
 import shlex
 import logging
+import argparse
 import subprocess
 
 
@@ -1074,8 +1075,6 @@ _distro = LinuxDistribution()
 
 
 def main():
-    import argparse
-
     logger = logging.getLogger(__name__)
     logger.setLevel(logging.DEBUG)
     logger.addHandler(logging.StreamHandler(sys.stdout))

tasks/vendoring/patches/distro.patch

@@ -1,21 +0,0 @@
-diff --git a/src/pip/_vendor/distro.py b/src/pip/_vendor/distro.py
-index 0afa527..9e7daad 100644
---- a/src/pip/_vendor/distro.py
-+++ b/src/pip/_vendor/distro.py
-@@ -34,7 +34,6 @@ import sys
- import json
- import shlex
- import logging
--import argparse
- import subprocess
- 
- 
-@@ -1052,6 +1051,8 @@ _distro = LinuxDistribution()
- 
- 
- def main():
-+    import argparse
-+
-     logger = logging.getLogger(__name__)
-     logger.setLevel(logging.DEBUG)
-     logger.addHandler(logging.StreamHandler(sys.stdout))