The color we were using didn't have enough contrast against a white
background, which made it harder to read texts like "Remove map marker"
or "Erase my account".
Since the new color is almost identical to the color we were using on
hover and for the border, we're changing the color on hover as well,
while IMHO it's no longer necessary to use a different color for the
border.
Using a button for interactive elements is better, as explained in
commit 5311daadf.
Since buttons with "type=button" do nothing by default, we no longer
need to call `preventDefault()` when clicking it.
We were using `map_location` in one place and
`location-map-remove-marker` in another one. We usually use dashes in
HTML class names, we don't say "location map" anywhere else.
