change(fastapi): refactor database ORM model definitions

We don't want to depend on the database to load up data
about the models we define. We now leverage the existing
`aurweb.schema` module for table definitions and set
__table_args__["autoload"] to False.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/models/package_source.py

@@ -1,22 +1,22 @@
-from sqlalchemy import Column, ForeignKey, Integer
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import backref, relationship
 
+from aurweb import schema
 from aurweb.models.declarative import Base
 from aurweb.models.package import Package as _Package
 
 
 class PackageSource(Base):
-    __tablename__ = "PackageSources"
+    __table__ = schema.PackageSources
+    __tablename__ = __table__.name
+    __mapper_args__ = {
+        "primary_key": [__table__.c.PackageID]
+    }
 
-    PackageID = Column(Integer, ForeignKey("Packages.ID", ondelete="CASCADE"),
-                       nullable=False)
     Package = relationship(
         _Package, backref=backref("package_sources", lazy="dynamic",
                                   cascade="all, delete"),
-        foreign_keys=[PackageID])
-
-    __mapper_args__ = {"primary_key": [PackageID]}
+        foreign_keys=[__table__.c.PackageID])
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)