I just installed my own 2016 Giant Contact SL Switch dropper post in the internal cable routing mode this week.
The simple answer is you would be best advised to just remove the seat itself by undoing the clamp bolts with the appropriate hex wrench, leaving the post itself installed in the frame. If that solution does not sufice, then opt for external cable routing, or give the folowing a try...
Long answer (Not recommended):
To remove the post you would have to loosen the set screw on the handlebar switch that fixes the inner cable. Since the set screw tends to crush the cable, it may not thread out of the housing well or thread back in easily (requiring replacement of the cable...).
If the cable end isn't totally crushed/unusable, then pull the section of housing away from the switch and put the short section of adjustable length housing in your pocket. Now you have to simultaneously lift the seat post out while pushing the housing through the frame from the handle bar side, ensuring the housing does not get pushed through the internal routing port into the frame downtube. If you don't have sufficient housing length between the handle bar and the port, then try pushing the cable through as much as you can for a little extra wiggle room. If the post is now completely outside of the seat tube, then you can just disengae the cable from the bracket on the post (no tools required).
The problem then is reinstallation of the post. You would have to re-engage the inner cable to the post (possibly having to invert the bike to get the bobbin to slid to the end of the cable), and then reinsert the post and reverse the earlier process - this time pulling housing/cable back through while lowering the post in. Then you have to put the length of adjustable housing back on and clamp the cable at the switch. Of course, as stated earlier the cable may need to be replaced it the end is too crushed.
All in all, much too much work to repeat. Hopefulyl just removing the seat from the post is sufficient, and you don't have to remove the post entirely. Because with the internal cable routing removing the post is cumbersome/likely something you only do once. External routing of the housing/cable would make the job easier.
In that situation you could get away with leaving the cable a bit long, taking up tension with the adjustable housing section, and then just loosening the adjustable housing and un-clipping the cable from the post to remove the post. Probably. You'd have to try it and see!