Remove tests requiring sqlalchemy > 0.7.8
See https://bitbucket.org/zzzeek/alembic/commits/d9fc0f82a298a858d9412fe0b270e640639dcc7a

diff -Naur alembic-0.4.2.orig/tests/test_autogenerate.py alembic-0.4.2/tests/test_autogenerate.py
--- alembic-0.4.2.orig/tests/test_autogenerate.py	2013-01-11 16:12:49.000000000 +0000
+++ alembic-0.4.2/tests/test_autogenerate.py	2013-03-15 12:43:52.881966999 +0000
@@ -1,6 +1,6 @@
 from sqlalchemy import MetaData, Column, Table, Integer, String, Text, \
     Numeric, CHAR, ForeignKey, DATETIME, \
-    TypeDecorator, CheckConstraint, Unicode, Enum,\
+    TypeDecorator, CheckConstraint, Unicode,\
     UniqueConstraint, Boolean, ForeignKeyConstraint
 from sqlalchemy.types import NULLTYPE, TIMESTAMP
 from sqlalchemy.dialects import mysql
@@ -1070,20 +1070,4 @@
             "existing_server_default='5')"
         )
 
-    def test_render_enum(self):
-        eq_ignore_whitespace(
-            autogenerate._repr_type(
-                        "sa.",
-                        Enum("one", "two", "three", name="myenum"),
-                        self.autogen_context),
-            "sa.Enum('one', 'two', 'three', name='myenum')"
-        )
-        eq_ignore_whitespace(
-            autogenerate._repr_type(
-                        "sa.",
-                        Enum("one", "two", "three"),
-                        self.autogen_context),
-            "sa.Enum('one', 'two', 'three')"
-        )
-
 # TODO: tests for dialect-specific type rendering + imports
diff -Naur alembic-0.4.2.orig/tests/test_op.py alembic-0.4.2/tests/test_op.py
--- alembic-0.4.2.orig/tests/test_op.py	2013-01-11 16:12:49.000000000 +0000
+++ alembic-0.4.2/tests/test_op.py	2013-03-15 12:46:13.362695693 +0000
@@ -457,13 +457,6 @@
         "DROP INDEX ik_test"
     )
 
-def test_drop_index_schema():
-    context = op_fixture()
-    op.drop_index('ik_test', schema='foo')
-    context.assert_(
-        "DROP INDEX foo.ik_test"
-    )
-
 def test_drop_table():
     context = op_fixture()
     op.drop_table('tb_test')