Fix branch remove for branches containing a '/'

##### What does this MR do?

This PR removed the DOM lookup for the branch name. This is not necessary, because the element already gets a `hidden` style applied.

##### Are there points in the code the reviewer needs to double check?

This adds a testcase, but this will fail currently. It depends on having the branch `improve/awesome` on the sample repository. See https://github.com/gitlabhq/testme/issues/6

##### Why was this MR needed?

If the branch name contains an invalid jQuery character like `/` the lookup for this element fails. As a result the element not gets removed from the DOM --> stale UX

/cc @jvanbaarsen