Remove assumption of gtm alias.

This script was assuming the presence of a "gtm" alias in the user
environment, mapping to:

                        $gtm_dist/mumps -dir

In this change we remove that assumption and explicitly compose the
command by using the "gtm_dist" environment variable.

This change facilitates the packaging of VistA for Debian Linux.

Change-Id: I4f9bd1505514c907be820a2fdb366ef596514281