Support: clean up comments and Support notation

I tried to get the comments in a similar format, and tried to update the `// Supports` to reflect the current browser reality by testing the bugs out in Browserstack. Those comments were about half with spaces and half without, I took out the spaces but now I think I might want them everywhere instead.

There are only comment changes here, although it reveals at least one chunk of code that could be removed from ajax.js if the comment was correct. That we can do in a separate commit.

In a few places we had redundant `// Supports` comments in both the supports.js and the point where the `support` property was used; several were out of sync. I opted to remove the ones at the point of use and keep them in supports.js for the most part.
@mzgol I spent some time Googling, and it seems like iOS 3 usage is too low to measure. The last time people really seemed to mention it was in 2012. The consensus then seemed to be: "leave it behind". Perhaps 1.x could keep support, while 2.x moved on?