Drop incorrect text class from text-line

[matthijsmelissen]

This saves 4 out 20 seconds on ever Carto-run on my system, and was a bug
anyway.

See also #1941.

[rrzefox]

It also decreases the size of the resulting .xml by more than 150 kB for me, which is impressive.

[pnorman]

Isn't this used in water-features.mss?

.text {
  [feature = 'waterway_dam'],
  [feature = 'waterway_weir'] {
    #text-poly[zoom >= 15],
    #text-line[zoom >= 15],
    #text-point[zoom >= 17] {
      ...
      #text-poly {
        ...
      }
      #text-line {
        ...
      }
      #text-point {
        ...
      }
    }
  }

  [feature = 'man_made_breakwater'][zoom >= 15],
  [feature = 'man_made_groyne'][zoom >= 15],
  [feature = 'man_made_pier'][zoom >= 15] {
    #text-poly,
    #text-line {
      ...
      #text-poly {
        ...
      }
      #text-line {
        ...
      }
    }
  }
}

[matthijsmelissen]

Yes, thanks for catching.

[matthijsmelissen]

Fixed, performance speed-up is still the same.

[matthijsmelissen]

@pnorman Could you review this and #1947 by any chance?