What is this 'slow-moving grey smoke' Skyrim player effect?

You can remove all applied spells by using player.DispelAllSpells, I believe. Note that this will also remove blessings and apparel effects, so you will need to unequip and re-equip armor to re-apply the effects from armor.

Try resolving the problem using a 'Cure All' batch file.
These files list all known active effects from the base game and DLC (and the Wet & Cold and Skyrim Immersive Creatures mods), preceded by the player.sme command (which stands for 'Stop Magic Effect' on 'player'), and can be executed using the in-game console.

You can find an archive file with these batch files under Solution 4 on this page. Here is a direct link (you need a (free) account in order to download). The file was created by NexusForums user LubitelSofta.
Be sure to take off all your (enchanted) gear beforehand.

Instructions as per the Nexus forum thread:

• Extract the files to your Skyrim root folder (not the data subfolder).
• Edit the Dawnguard, Dragonborn, or WC or SIC batch files (if necessary) so that every shader or effect ID matches your load order (see above).
• Start the game.
• In the console type bat <filename> (without quotes), e.g. bat DBMGEF.