Remove NASAGIBS Blue Marble example (#1918)

* Remove NASAGIBS Blue Marble example

* update docstrings

Author: Conengmo

folium/folium.py

@@ -90,16 +90,13 @@ class Map(JSCSSMixin, MacroElement):
         - "OpenStreetMap"
         - "CartoDB Positron"
         - "CartoDB Voyager"
-        - "NASAGIBS Blue Marble"
 
-    You can pass a custom tileset to Folium by passing a
-    :class:`xyzservices.TileProvider` or a Leaflet-style
-    URL to the tiles parameter: ``http://{s}.yourtiles.com/{z}/{x}/{y}.png``.
+    Explore more provider names available in ``xyzservices`` here:
+    https://leaflet-extras.github.io/leaflet-providers/preview/.
 
-    You can find a list of free tile providers here:
-    ``http://leaflet-extras.github.io/leaflet-providers/preview/``.
-    Be sure to check their terms and conditions and to provide attribution
-    with the `attr` keyword.
+    You can also pass a custom tileset by passing a
+    :class:`xyzservices.TileProvider` or a Leaflet-style
+    URL to the tiles parameter: ``https://{s}.yourtiles.com/{z}/{x}/{y}.png``.
 
     Parameters
     ----------

folium/raster_layers.py

@@ -33,16 +33,13 @@ class TileLayer(Layer):
             - "OpenStreetMap"
             - "CartoDB Positron"
             - "CartoDB Voyager"
-            - "NASAGIBS Blue Marble"
 
-        You can pass a custom tileset to Folium by passing a
-        :class:`xyzservices.TileProvider` or a Leaflet-style
-        URL to the tiles parameter: ``http://{s}.yourtiles.com/{z}/{x}/{y}.png``.
+        Explore more provider names available in ``xyzservices`` here:
+        https://leaflet-extras.github.io/leaflet-providers/preview/.
 
-        You can find a list of free tile providers here:
-        ``http://leaflet-extras.github.io/leaflet-providers/preview/``.
-        Be sure to check their terms and conditions and to provide attribution
-        with the `attr` keyword.
+        You can also pass a custom tileset by passing a
+        :class:`xyzservices.TileProvider` or a Leaflet-style
+        URL to the tiles parameter: ``https://{s}.yourtiles.com/{z}/{x}/{y}.png``.
     min_zoom: int, default 0
         Minimum allowed zoom level for this tile layer.
     max_zoom: int, default 18