web/components: drop the stale button height overrides
the star and fork controls hand-rolled their own joined-group wrapper and then
forced their buttons to min-h-7.5 to fit inside a max-h-8 box, so they came out
shorter than every other button on the platform. both now use ButtonGroup, which
does the radius collapsing and border overlap already, and the buttons keep
their own size, and the signed-out stars link becomes a Button instead of an
anchor styled to look like one.
measured on the repo header story: the stars control and the fork pair are both
34px now, where the pair used to be 36px and its segments 30px.
Signed-off-by: eti <eti@eti.tf>