Fix: Remove extra mappings

Actually we don't need thess mappings, because that's only an internal
information. If it's needed in the future please revert this commit with
correct mappings.

Resolves: #1

app/repositories/models.py

@@ -179,14 +179,6 @@ class EpisodeCharacterAssociation(Base):
         primary_key=True,
     )
 
-    character: Mapped["Character"] = relationship(
-        back_populates="episode_associations",
-    )
-
-    episode: Mapped["Episode"] = relationship(
-        back_populates="character_associations",
-    )
-
 
 class Episode(Base):
     __tablename__ = "episodes"
@@ -247,10 +239,6 @@ class Episode(Base):
         back_populates="episodes",
     )
 
-    character_associations: Mapped[List["EpisodeCharacterAssociation"]] = relationship(
-        back_populates="episode",
-    )
-
 
 class EpisodeDoesNotExist(Exception):
     """Episode does not exist."""
@@ -328,9 +316,6 @@ class Character(Base):
         secondary="episode_character_association",
         back_populates="characters",
     )
-    episode_associations: Mapped[List["EpisodeCharacterAssociation"]] = relationship(
-        back_populates="character",
-    )
 
 
 class CharacterDoesNotExist(Exception):