remove isolate_from_table for dropconstraint

Revised the change regarding SQLAlchemy 2.1 and deprecation warnings
related to ``isolate_from_table=True``. Further developments in release 2.1
have revised how this parameter will be modified.

Change-Id: I6af2a683660647980421b1ff761dcf53a61bb71a

Author: zzzeek

alembic/ddl/impl.py

@@ -412,12 +412,11 @@ def drop_column(
     def add_constraint(self, const: Any, **kw: Any) -> None:
         if const._create_rule is None or const._create_rule(self):
             if sqla_compat.sqla_2_1:
+                # this should be the default already
                 kw.setdefault("isolate_from_table", True)
             self._exec(schema.AddConstraint(const, **kw))
 
     def drop_constraint(self, const: Constraint, **kw: Any) -> None:
-        if sqla_compat.sqla_2_1:
-            kw.setdefault("isolate_from_table", True)
         self._exec(schema.DropConstraint(const, **kw))
 
     def rename_table(

docs/build/changelog.rst

@@ -60,14 +60,19 @@ Changelog
         commands.
 
     .. change::
-        :tags: usecase
+        :tags: usecase, operations
 
         Avoid deprecation warning in add/drop constraint added in SQLAlchemy 2.1.
         Ensure that alembic is compatible with the changes added in
         https://github.com/sqlalchemy/sqlalchemy/issues/13006
         by explicitly setting ``isolate_from_table=True`` when running with
         SQLAlchemy 2.1 or greater.
 
+        .. note::
+
+           This change was revised in Alembic 1.18.1; futher developments
+           in SQLAlchemy 2.1 necessitated further adjustments.
+
     .. change::
         :tags: feature, autogenerate
 

docs/build/unreleased/constraint_dep_revert.rst

@@ -0,0 +1,7 @@
+.. change::
+    :tags: bug, operations
+
+    Revised the change regarding SQLAlchemy 2.1 and deprecation warnings
+    related to ``isolate_from_table=True``. Further developments in release 2.1
+    have revised how this parameter will be modified.
+