remove provider_rates table

this was added five years ago but never used. if we want to bring back
variable rates per client we might as well get a fresh start since a lot
has changed since then.

migrations/versions/0372_remove_provider_rates.py

@@ -0,0 +1,30 @@
+"""
+
+Revision ID: 0372_remove_provider_rates
+Revises: 0371_fix_apr_2022_sms_rate
+Create Date: 2022-04-26 09:39:45.260951
+
+"""
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = '0372_remove_provider_rates'
+down_revision = '0371_fix_apr_2022_sms_rate'
+
+
+def upgrade():
+    op.drop_table('provider_rates')
+
+
+def downgrade():
+    op.create_table(
+        'provider_rates',
+        sa.Column('id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('valid_from', sa.DateTime(), nullable=False),
+        sa.Column('provider_id', postgresql.UUID(as_uuid=True), nullable=True),
+        sa.Column('rate', sa.Numeric(), nullable=False),
+        sa.PrimaryKeyConstraint('id'),
+        sa.ForeignKeyConstraint(['provider_id'], ['provider_details.id'], ),
+    )