remove incorrect quoting of variable value

This being make, the original implementation caused the value of the
make variable COMPOSE_PROJECT_NAME to _include the surrounding
double-quotes_, and this _happened_ to work just because we were using
this variable in shell commands, where the quoting would be handled as
normal CLI quoting of a string. However, since we _also_ make this make
variable available as environment variable (through the `export` command
through which we set env vars from a dotenv file), this ended up
breaking things from Compose v2.4 through this change:
docker/compose#9332.

Makefile

@@ -20,7 +20,7 @@ DOCKER_CLEAN_VOLUMES := $(if $(environment), , \
 	docker volume rm -f marxan-cloud_marxan-cloud-postgresql-api-data && \
 	docker volume rm -f marxan-cloud_marxan-cloud-postgresql-geo-data && \
 	docker volume rm -f marxan-cloud_marxan-cloud-redis-api-data )
-COMPOSE_PROJECT_NAME := "marxan-cloud"
+COMPOSE_PROJECT_NAME := marxan-cloud
 
 ## some color to give live to the outputs
 RED :=\033[1;32m