Bump the minimum PyPy/cffi version and simplify as a result (#3585)

* Bump the minimum PyPy/cffi version and simplify as a result

* unused imports

* grumble, fix
diff --git a/setup.py b/setup.py
index 33b3b54..b134e0a 100644
--- a/setup.py
+++ b/setup.py
@@ -47,14 +47,14 @@
     requirements.append("ipaddress")
 
 if platform.python_implementation() == "PyPy":
-    if sys.pypy_version_info < (2, 6):
+    if sys.pypy_version_info < (5, 3):
         raise RuntimeError(
-            "cryptography 1.0 is not compatible with PyPy < 2.6. Please "
+            "cryptography 1.9 is not compatible with PyPy < 5.3. Please "
             "upgrade PyPy to use this library."
         )
 else:
-    requirements.append("cffi>=1.4.1")
-    setup_requirements.append("cffi>=1.4.1")
+    requirements.append("cffi>=1.7")
+    setup_requirements.append("cffi>=1.7")
 
 test_requirements = [
     "pytest>=2.9.0",