Don't count both SYS and NEVM disk space requirements

[ConanMishler]

When builder.py calculates disk space requirements for the chosen SNode configuration, if both SYS and NEVM services have been selected for deployment, it currently adds the required space for SYS and also the required space for NEVM when calculating the total disk space required. It should never add the disk space required for NEVM because it's the same disk space used by SYS (and if NEVM is sourced externally, there is also no local disk space required for NEVM).