Stop using a suboptimal structure for Vector's variants menu

One label is enough.

We need to keep the styles and some inline hacks in the HTML for a
while to keep current CSS compatible with old HTML, which is cached in
WMF environment for up to 30 days.

Follow-up to clean up the mess: I2817c6e9eb52ffc785a04bb9d23b0802a553fd45.

Bug: 43406
Change-Id: Idf43d77dccff83ad81db776f3262e0ef12d25c92
Merge "Stop using a suboptimal structure for Vector's variants menu"