The way the terminators on these drives work is that all lines of the floppy interface are open-collector drive. If you look on the floppy controller and drive PCBs, you'll probably see some 7438 open-collector NAND buffers. These have a maximum drive capability of 48 ma at 5v. Your terminators are 150 ohm pullups.
For the sake of argument, let's suppose that the output transistor in a 7438 drops about a volt. So you have 4V into 150 ohms for a drive set with a single terminator or 75 ohms if two terminators are used. The current used respectively is about 27 or 53 ma, the latter being somewhat higher than the rated current for the 7438 drivers. Not fatal, but unnecessarily hard on the IC. Best to terminate as per standard practice and leave just one terminator installed. You could even safely use a 470 ohm terminator and it wouldn't affect a thing, given the drive cable length.
Later floppies use LS-series TTL or CMOS logic and use much higher (2K) pullups which can be left permanently installed. The original 150 ohm terminator value was inherited from the 8" drive standards that could employ long cables (look at the number of old systems with external 8" drives). That's not the case here.
