In targets.json, ARM_MUSCA_B1 and ARM_MUSCA_S1 have alias target
names suffixed with `_NS`. They are identical to targets without
`_NS` and exist purely for compatibility with the old naming
convention we had. The CI builds them as separate targets and uses
extra resources.

As we are upgrading Musca targets to TF-M v1.2, it's time to clean
up the aliases.