fix: don't override paths in dockerfile

This allows for these paths to continue to be set in the config file or environment variable while still maintaining the default of having the default paths in the same directory as the postal config file.

Dockerfile

@@ -48,9 +48,6 @@ RUN echo $VERSION > VERSION
 
 # Set paths for when running in a container
 ENV POSTAL_CONFIG_FILE_PATH=/config/postal.yml
-ENV POSTAL_SIGNING_KEY_PATH=/config/signing.key
-ENV SMTP_SERVER_TLS_CERTIFICATE_PATH=/config/smtp.cert
-ENV SMTP_SERVER_TLS_PRIVATE_KEY_PATH=/config/smtp.key
 
 # Set the CMD
 ENTRYPOINT [ "/docker-entrypoint.sh" ]