Remove "number of sockets" from plug data submission/model

[stuartpb]

Honestly, this would just be one less piece of complex / hard-to-quantify friction in submitting the plug.

User stories with "number of plugs" as a datum:

• "There are three plates, and this one has four outlets, but this one's powering the lamp and this one's powering a TV and somebody's usually using the... eh, forget it."
• "Okay, so I'm adding a plug entry for these tree outlets... huh. There's a 2-socket outlet on each tree, and there are like... 20 trees? So am I supposed to put 40, or am I supposed to make a submission for each tree? That'd be a lot of work, but 40 outlets would probably throw off, like, an algorithm... ah, forget it."

User stories without it:

• "Here's a photo and a tagline, tap submit and done."
• "Looks like there's one at Starbucks. How many outlets will be available? Eh, I really only need one."

How many outlets are available doesn't realistically matter in any practical use case. If you care about having multiple outlets available to you, you should be carrying around a duplexer or something.

Plus, if this ends up actually needing to be quantified, you can pretty much just do it post-facto from the photos with a Mechanical Turk task (where you have better / more reliable control over the data anyway).