Revert "[AIRFLOW-3014] Increase max length of connection password column to 5000 (#6241)" (#6783)

This reverts commit da7a353e17.

This was already fixed by by #6754 which was already merged, and we ended up with
two migration files (trying) to do the same thing.

airflow/migrations/versions/c1840b4bcf1a_increase_length_of_password_column_in_.py

@@ -1,50 +0,0 @@
-#
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#   http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing,
-# software distributed under the License is distributed on an
-# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
-# KIND, either express or implied.  See the License for the
-# specific language governing permissions and limitations
-# under the License.
-
-"""Increase length of password column in connection table
-
-Revision ID: c1840b4bcf1a
-Revises: 004c1210f153
-Create Date: 2019-10-02 16:56:54.865550
-
-"""
-
-import sqlalchemy as sa
-from alembic import op
-
-# revision identifiers, used by Alembic.
-revision = 'c1840b4bcf1a'
-down_revision = '004c1210f153'
-branch_labels = None
-depends_on = None
-
-
-def upgrade():
-    conn = op.get_bind()
-    if conn.dialect.name == 'sqlite':
-        # SQLite does not allow column modifications so we need to skip this migration
-        return
-
-    op.alter_column(table_name='connection',
-                    column_name='password',
-                    type_=sa.String(length=5000))
-
-
-def downgrade():
-    # Can't be undone
-    pass