Update Python version support. (rapidsai#2363)

This PR updates Python version classifiers and conda environments to use the versions of Python currently supported by RAPIDS (3.8, 3.9).

I also removed `readthedocs.yml` because it seems out of date and points to a conda environment that no longer exists.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - AJ Schmidt (https://github.com/ajschmidt8)
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Rick Ratzel (https://github.com/rlratzel)

URL: rapidsai#2363

SOURCEBUILD.md

@@ -236,7 +236,7 @@ Run either the C++ or the Python tests with datasets
    make test
    ```
 
-Note: This conda installation only applies to Linux and Python versions 3.7/3.8.
+Note: This conda installation only applies to Linux and Python versions 3.8/3.9.
 
 ### Building and Testing on a gpuCI image locally
 

conda/environments/cugraph_dev_cuda11.2.yml

@@ -26,7 +26,7 @@ dependencies:
 - clang=11.1.0
 - clang-tools=11.1.0
 - cmake>=3.20.1,!=3.23.0
-- python>=3.6,<3.9
+- python>=3.8,<3.10
 - notebook>=0.5.0
 - boost
 - cython>=0.29,<0.30

conda/environments/cugraph_dev_cuda11.4.yml

@@ -26,7 +26,7 @@ dependencies:
 - clang=11.1.0
 - clang-tools=11.1.0
 - cmake>=3.20.1,!=3.23.0
-- python>=3.6,<3.9
+- python>=3.8,<3.10
 - notebook>=0.5.0
 - boost
 - cython>=0.29,<0.30

conda/environments/cugraph_dev_cuda11.5.yml

@@ -26,7 +26,7 @@ dependencies:
 - clang=11.1.0
 - clang-tools=11.1.0
 - cmake>=3.20.1,!=3.23.0
-- python>=3.6,<3.9
+- python>=3.8,<3.10
 - notebook>=0.5.0
 - boost
 - cython>=0.29,<0.30

python/cugraph/setup.py

@@ -183,8 +183,8 @@ def finalize_options(self):
           "Intended Audience :: Developers",
           # "Operating System :: OS Independent",
           "Programming Language :: Python",
-          "Programming Language :: Python :: 3.6",
-          "Programming Language :: Python :: 3.7"
+          "Programming Language :: Python :: 3.8",
+          "Programming Language :: Python :: 3.9"
       ],
       # Include the separately-compiled shared library
       author="NVIDIA Corporation",

python/pylibcugraph/setup.py

@@ -140,8 +140,8 @@ def run(self):
           "Intended Audience :: Developers",
           # "Operating System :: OS Independent",
           "Programming Language :: Python",
-          "Programming Language :: Python :: 3.6",
-          "Programming Language :: Python :: 3.7"
+          "Programming Language :: Python :: 3.8",
+          "Programming Language :: Python :: 3.9"
       ],
       # Include the separately-compiled shared library
       author="NVIDIA Corporation",