Remove webgl heatmap, as it doesn't work right.

It's a shame it doesn't do what we want - looks like we'll have to find 
another one.....

.gitmodules

@@ -1,6 +1,3 @@
 [submodule "lantern-build-engine"]
 	path = lantern-build-engine
 	url = https://gitlab.com/sbrl/lantern-build-engine.git
-[submodule "lib/webgl-heatmap"]
-	path = lib/webgl-heatmap
-	url = https://github.com/pyalot/webgl-heatmap.git

lib/webgl-heatmap

@@ -1 +0,0 @@
-Subproject commit 995d541b13a84e6b3877468c0244371d2832a3c5

package.json

@@ -20,7 +20,6 @@
     "leaflet": "^1.4.0",
     "leaflet-fullscreen": "^1.0.2",
     "leaflet-timedimension": "^1.1.0",
-    "leaflet-webgl-heatmap": "^0.2.7",
     "leaflet.markercluster": "^1.4.1"
   },
   "devDependencies": {