Remove generic "ParseError" from Tile.cs

[david-rhodes]

Reference: mapbox/mapbox-unity-sdk#45

VectorTile.cs sets an error if unable to parse the byte data:

                internal override bool ParseTileData(byte[] data)
		{
			try
			{
				var decompressed = Compression.Decompress(data);
				this.data = new Mapbox.VectorTile.VectorTile(decompressed);

				return true;
			}
			catch (Exception ex)
			{
                Debug.Log("VectorTile: " + "WTF");
				SetError("VectorTile parsing failed: " + ex.ToString());
				return false;
			}
		}

but the error is then overridden in Tile.cs:

else if (this.ParseTileData(response.Data) == false)
{
	this.error = "ParseError";
}

[wilhelmberg]

Done in #75