Is there a term for the "no base building" levels in real-time strategy games?
Solution 1:
I would think the term RTT (real time tactics) would be a good fit. It is a sub/related genre to RTS, and is "focused on tactical and operational aspects of warfare such as unit formations or the exploitation of terrain for tactical advantage" as opposed to the "logistics and production".
I have also heard the terms non-base building used fairly frequently. Alternatively, I've heard the term "Call ins" used to refer to games where you simply call in the troops you need to fight with as opposed to building them.