Move npm config setting to the conda buildpack

Since everything is based off the conda buildpack now,
and that is where we get npm from

repo2docker/buildpacks/base.py

@@ -616,32 +616,8 @@ class BaseImage(BuildPack):
         """Return env directives required for build"""
         return [
             ("APP_BASE", "/srv"),
-            ("NPM_DIR", "${APP_BASE}/npm"),
-            ("NPM_CONFIG_GLOBALCONFIG", "${NPM_DIR}/npmrc"),
         ]
 
-    def get_path(self):
-        return super().get_path() + ["${NPM_DIR}/bin"]
-
-    def get_build_scripts(self):
-        scripts = [
-            (
-                "root",
-                r"""
-                mkdir -p ${NPM_DIR} && \
-                chown -R ${NB_USER}:${NB_USER} ${NPM_DIR}
-                """,
-            ),
-            (
-                "${NB_USER}",
-                r"""
-                npm config --global set prefix ${NPM_DIR}
-                """,
-            ),
-        ]
-
-        return super().get_build_scripts() + scripts
-
     def get_env(self):
         """Return env directives to be set after build"""
         return []

repo2docker/buildpacks/conda/__init__.py

@@ -33,6 +33,9 @@ class CondaBuildPack(BaseImage):
         env = super().get_build_env() + [
             ("CONDA_DIR", "${APP_BASE}/conda"),
             ("NB_PYTHON_PREFIX", "${CONDA_DIR}/envs/notebook"),
+            # We install npm / node from conda-forge
+            ("NPM_DIR", "${APP_BASE}/npm"),
+            ("NPM_CONFIG_GLOBALCONFIG", "${NPM_DIR}/npmrc"),
         ]
         if self.py2:
             env.append(("KERNEL_PYTHON_PREFIX", "${CONDA_DIR}/envs/kernel"))
@@ -55,6 +58,8 @@ class CondaBuildPack(BaseImage):
         if self.py2:
             path.insert(0, "${KERNEL_PYTHON_PREFIX}/bin")
         path.insert(0, "${NB_PYTHON_PREFIX}/bin")
+        # This is at the end of $PATH, for backwards compat reasons
+        path.append("${NPM_DIR}/bin")
         return path
 
     def get_build_scripts(self):
@@ -83,7 +88,20 @@ class CondaBuildPack(BaseImage):
                 bash -c 'time /tmp/install-miniforge.bash' && \
                 rm /tmp/install-miniforge.bash /tmp/environment.yml
                 """,
-            )
+            ),
+            (
+                "root",
+                r"""
+                mkdir -p ${NPM_DIR} && \
+                chown -R ${NB_USER}:${NB_USER} ${NPM_DIR}
+                """,
+            ),
+            (
+                "${NB_USER}",
+                r"""
+                npm config --global set prefix ${NPM_DIR}
+                """,
+            ),
         ]
 
     major_pythons = {"2": "2.7", "3": "3.7"}