patman: Drop Python 2 StringIO code

We can rely on Python 3 now, so drop the workaround for importing
StringIO.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/func_test.py b/tools/patman/func_test.py
index 76319ff..748e225 100644
--- a/tools/patman/func_test.py
+++ b/tools/patman/func_test.py
@@ -12,10 +12,7 @@
 import tempfile
 import unittest
 
-try:
-    from StringIO import StringIO
-except ImportError:
-    from io import StringIO
+from io import StringIO
 
 import gitutil
 import patchstream
diff --git a/tools/patman/settings.py b/tools/patman/settings.py
index 9ac96c4..21e8fc4 100644
--- a/tools/patman/settings.py
+++ b/tools/patman/settings.py
@@ -34,10 +34,7 @@
     - Merge general default settings/aliases with project-specific ones.
 
     # Sample config used for tests below...
-    >>> try:
-    ...     from StringIO import StringIO
-    ... except ImportError:
-    ...     from io import StringIO
+    >>> from io import StringIO
     >>> sample_config = '''
     ... [alias]
     ... me: Peter P. <likesspiders@example.com>
diff --git a/tools/patman/test_util.py b/tools/patman/test_util.py
index 4338dbc..4d0085e 100644
--- a/tools/patman/test_util.py
+++ b/tools/patman/test_util.py
@@ -10,10 +10,7 @@
 
 import command
 
-try:
-  from StringIO import StringIO
-except ImportError:
-  from io import StringIO
+from io import StringIO
 
 PYTHON = 'python%d' % sys.version_info[0]