simplify remote fixtures scripts

[seawolf42]

Remove XXX_fixtures.sh files are replace with a single get_remote_fixtures.sh file that takes a single parameter, the database to use:

get_remote_fixtures.sh $DATABASE_URL

Then when calling the script, get the value of the variable using heroku's command for this:

heroku config:get DATABASE_URL -a <project>-<environment>

Then simplify the make command to:

make fixtures.remote.<environment>