[Docs] Remove GNSS Debug support flag
[Docs] Remove GNSS Debug support flag

Removed indication that LE_GNSS_NMEA_MASK_DEBUG is
supported for the AR758x/AR759x devices.

Resolves: LE-9979
Change-Id: I0d243c1d74f59a03e7e20882a3d4afea14963dd3

legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af