Remove names from short road segments

[nvkelso]

In #2008 we stripped names from roads per kind of road and zoom. But that still yields names on short road segments which don't have enough room to actually label.

After roads are merged, we should evaluate if the merged features are long enough to have the name actually label, and if it's not long enough drop the names.

Then we should merge features again so the newly nameless roads merge together.

We do this same trick in the boundaries layer already, so reprise that here:

• https://github.com/tilezen/vector-datasource/blob/v1.8.0/queries.yaml#L763-L794

[nvkelso]

Additionally we should evaluate dropping features with very short length during the new merge, similar to:

• https://github.com/tilezen/vector-datasource/blob/v1.8.0/queries.yaml#L1684-L1709

Where we use different drop_length_pixels config for:

drop_short_segments: true
drop_length_pixels: 0.1

[nvkelso]

Fixed via #2031.