[docs] Remove usage of non-existent margin jss class

[G-Rath]

• I have followed (at least) the PR section of the contributing guide.

[eps1lon]

Discovered this as well while porting the demos to typescript. Well spotted 👍

[G-Rath]

Discovered this as well while porting the demos to typescript. Well spotted 👍

I was literally just thinking that that might be a good idea, as I found these by using them in my TypeScript project 😂

I've also just found another one in the same file:

https://github.com/mui-org/material-ui/blob/06967ec3b2d01ff245879ffca8650471525a36f8/docs/src/pages/demos/app-bar/PrimarySearchAppBar.js#L120-L130

The MenuItems here are using the wrong function name for onClick! I'll make a seperate PR, as I'm too lazy to check the project out & can't make another commit via GitHubs editor 😕

(Unless @oliviertassinari you'd like to do it, and push the commit to this branch/PR?)

[oliviertassinari]

I'm too lazy to check the project out & can't make another commit via GitHubs editor

@G-Rath I can see that :p

[G-Rath]

@oliviertassinari in my defence, I make the edits as I find them during my normal usage of the docs, so I didn't expect to make that many :P

I've stopped being lazy, and made a new commit locally correcting the onClick function. I also checked out the rest of the app-bar examples; they're all fine.

Feel free to merge 😄

[oliviertassinari]

@G-Rath It's perfect, well done :)