Replace Reviewer Label/Hashtag close image with better char

The previous character:
 ☒
...would look funny on certains OSes and missing on other.

Replaced with:
 ×

Skipped the CSS-border. Looks better without.

Change-Id: Ia3c3515365fd6dce4d9b15b1b37f587d6e17371d
2 files changed