Revert "Cache downloaded data in zc/buildout/buildout.py:_open() in memory to...

Revert "Cache downloaded data in zc/buildout/buildout.py:_open() in memory to accelerate remote extends."

This reverts commit 260bc0c4 partially.

The remaining should be squashed with "Write .installed.cfg only once, in safe way and only if there's any change."

src/zc/buildout/buildout.py

@@ -1813,7 +1813,6 @@ def _default_globals():
 
     return globals_defs
 
-_open_download_cache = {}
 def _open(base, filename, seen, dl_options, override, downloaded):
     """Open a configuration file and return the result as a dictionary,
 
@@ -1843,14 +1842,8 @@ def _open(base, filename, seen, dl_options, override, downloaded):
             base = os.path.dirname(filename)
         else:
             filename = base + '/' + filename
-            data = _open_download_cache.get(filename)
-            if data is None:
-                downloaded_filename, is_temp = download(filename)
-                data = open(downloaded_filename).read()
-                _open_download_cache[filename] = data
-            else:
-                is_temp = False
-            fp = StringIO(data)
+            downloaded_filename, is_temp = download(filename)
+            fp = open(downloaded_filename)
             base = filename[:filename.rfind('/')]
     else:
         filename = os.path.join(base, filename)