update conda used for freezing and remove workaround for conda-export bug

Bug is fixed in conda 4.4

repo2docker/buildpacks/conda/freeze.py

@@ -15,6 +15,8 @@ from ruamel.yaml import YAML
 
 
 MINICONDA_VERSION = '4.3.27'
+# need conda ≥ 4.4 to avoid bug adding spurious pip dependencies
+CONDA_VERSION = '4.4.8'
 
 HERE = pathlib.Path(os.path.dirname(os.path.abspath(__file__)))
 
@@ -27,34 +29,6 @@ FROZEN_FILE_T = os.path.splitext(ENV_FILE_T)[0] + '.frozen.yml'
 yaml = YAML(typ='rt')
 
 
-def fixup(frozen_file):
-    """Fixup a frozen environment file
-
-    Conda export has a bug!
-    https://github.com/conda/conda/pull/6391
-    """
-    with open(frozen_file) as f:
-        env = yaml.load(f)
-
-    # scrub spurious pip dependencies
-    # due to conda #6391
-
-    # note: this scrubs *all* pip dependencies,
-    # so be more careful if we ever *want* conda to call
-    # out to pip.
-    pip_found = False
-    for idx, dep in enumerate(env['dependencies']):
-        if isinstance(dep, dict) and 'pip' in dep:
-            pip_found = True
-            break
-
-    if pip_found:
-        env['dependencies'].pop(idx)
-
-    with open(frozen_file, 'w') as f:
-        yaml.dump(env, f)
-
-
 def freeze(env_file, frozen_file):
     """Freeze a conda environment.yml
 
@@ -79,6 +53,7 @@ def freeze(env_file, frozen_file):
         f"continuumio/miniconda3:{MINICONDA_VERSION}",
         "sh", "-c",
         '; '.join([
+            f"conda install -yq conda={CONDA_VERSION}",
             'conda config --add channels conda-forge',
             'conda config --system --set auto_update_conda false',
             f"conda env create -v -f /r2d/{env_file} -n r2d",
@@ -88,7 +63,6 @@ def freeze(env_file, frozen_file):
             f"conda env export -n r2d >> /r2d/{frozen_file}",
         ])
     ])
-    fixup(HERE / frozen_file)
 
 
 def set_python(py_env_file, py):