Antd tab close button too BIG

[joshuef]

Looking at the two buttons for closing / opening tabs, the close button seems sooooo big.

Like, too big.

https://www.dropbox.com/s/m07e0lfzygjsocd/Screenshot%202018-12-20%2009.43.28.jpg?dl=0

Comparing that to chrome (https://www.dropbox.com/s/hy2jz6deh447v1j/Screenshot%202018-12-20%2009.46.40.jpg?dl=0), you can see that the close button is just a bit smaller.

@shriram2301 I think we should remove the 'button' aspect of this 'close' button, and use only the icon, and then make that icon, a bit smaller.

Note, the icon should still have a pointer on hover, and ideally some :hover css state to reflect this interact-ablity (as well as the click event/functionality).

[joshuef]

Just to note, this is currently tied to #669

[safesurfer]

QA verified