Clean up Dockerfile by removing unused npm installs

Removed unnecessary npm package installations for dotenv, pg, bcrypt, and jsonwebtoken.

srcs/backend/dockerfile

@@ -5,10 +5,6 @@ WORKDIR /app
 COPY package*.json ./
 
 RUN npm install
-RUN npm install dotenv
-RUN npm install pg
-RUN npm install bcrypt
-RUN npm install jsonwebtoken
 RUN npm install passport
 RUN npm install passport-github2
 RUN npm install express-session
@@ -19,4 +15,4 @@ EXPOSE 3001
 
 ENV NODE_ENV=development
 
-CMD ["node", "index.js"]
+CMD ["node", "index.js"]