build(python): remove python 3.7 from kokoro Dockerfile (#226)

Source-Link: https://github.com/googleapis/synthtool/commit/e44dc0c742b1230887a73552357e0c18dcc30b92
Post-Processor: gcr.io/repo-automation-bots/owlbot-python:latest@sha256:5ff7446edeaede81c3ed58b23a4e76a5403fba1350ce28478045657303b6479d
diff --git a/.github/.OwlBot.lock.yaml b/.github/.OwlBot.lock.yaml
index a5d3697..cb06536 100644
--- a/.github/.OwlBot.lock.yaml
+++ b/.github/.OwlBot.lock.yaml
@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/repo-automation-bots/owlbot-python:latest
-  digest: sha256:e1793a23ae0ee9aafb2e3a53b564a351f74790dbe3c2d75f8fc3b8c43e5c036c
+  digest: sha256:5ff7446edeaede81c3ed58b23a4e76a5403fba1350ce28478045657303b6479d
diff --git a/.kokoro/docker/docs/Dockerfile b/.kokoro/docker/docs/Dockerfile
index 412b0b5..4e1b1fb 100644
--- a/.kokoro/docker/docs/Dockerfile
+++ b/.kokoro/docker/docs/Dockerfile
@@ -40,6 +40,7 @@
     libssl-dev \
     libsqlite3-dev \
     portaudio19-dev \
+    python3-distutils \
     redis-server \
     software-properties-common \
     ssh \
@@ -59,40 +60,8 @@
   && rm -rf /var/lib/apt/lists/* \
   && rm -f /var/cache/apt/archives/*.deb
 
-
-COPY fetch_gpg_keys.sh /tmp
-# Install the desired versions of Python.
-RUN set -ex \
-    && export GNUPGHOME="$(mktemp -d)" \
-    && echo "disable-ipv6" >> "${GNUPGHOME}/dirmngr.conf" \
-    && /tmp/fetch_gpg_keys.sh \
-    && for PYTHON_VERSION in 3.7.8 3.8.5; do \
-        wget --no-check-certificate -O python-${PYTHON_VERSION}.tar.xz "https://www.python.org/ftp/python/${PYTHON_VERSION%%[a-z]*}/Python-$PYTHON_VERSION.tar.xz" \
-        && wget --no-check-certificate -O python-${PYTHON_VERSION}.tar.xz.asc "https://www.python.org/ftp/python/${PYTHON_VERSION%%[a-z]*}/Python-$PYTHON_VERSION.tar.xz.asc" \
-        && gpg --batch --verify python-${PYTHON_VERSION}.tar.xz.asc python-${PYTHON_VERSION}.tar.xz \
-        && rm -r python-${PYTHON_VERSION}.tar.xz.asc \
-        && mkdir -p /usr/src/python-${PYTHON_VERSION} \
-        && tar -xJC /usr/src/python-${PYTHON_VERSION} --strip-components=1 -f python-${PYTHON_VERSION}.tar.xz \
-        && rm python-${PYTHON_VERSION}.tar.xz \
-        && cd /usr/src/python-${PYTHON_VERSION} \
-        && ./configure \
-            --enable-shared \
-            # This works only on Python 2.7 and throws a warning on every other
-            # version, but seems otherwise harmless.
-            --enable-unicode=ucs4 \
-            --with-system-ffi \
-            --without-ensurepip \
-        && make -j$(nproc) \
-        && make install \
-        && ldconfig \
-  ; done \
-  && rm -rf "${GNUPGHOME}" \
-  && rm -rf /usr/src/python* \
-  && rm -rf ~/.cache/
-
 RUN wget -O /tmp/get-pip.py 'https://bootstrap.pypa.io/get-pip.py' \
-  && python3.7 /tmp/get-pip.py \
   && python3.8 /tmp/get-pip.py \
   && rm /tmp/get-pip.py
 
-CMD ["python3.7"]
+CMD ["python3.8"]
diff --git a/.kokoro/docker/docs/fetch_gpg_keys.sh b/.kokoro/docker/docs/fetch_gpg_keys.sh
deleted file mode 100755
index d653dd8..0000000
--- a/.kokoro/docker/docs/fetch_gpg_keys.sh
+++ /dev/null
@@ -1,45 +0,0 @@
-#!/bin/bash
-# Copyright 2020 Google LLC
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# A script to fetch gpg keys with retry.
-# Avoid jinja parsing the file.
-# 
-
-function retry {
-    if [[ "${#}" -le 1 ]]; then
-	echo "Usage: ${0} retry_count commands.."
-	exit 1
-    fi
-    local retries=${1}
-    local command="${@:2}"
-    until [[ "${retries}" -le 0 ]]; do
-	$command && return 0
-	if [[ $? -ne 0 ]]; then
-	    echo "command failed, retrying"
-	    ((retries--))
-	fi
-    done
-    return 1
-}
-
-# 3.6.9, 3.7.5 (Ned Deily)
-retry 3 gpg --keyserver ha.pool.sks-keyservers.net --recv-keys \
-      0D96DF4D4110E5C43FBFB17F2D347EA6AA65421D
-
-# 3.8.0 (Ɓukasz Langa)
-retry 3 gpg --keyserver ha.pool.sks-keyservers.net --recv-keys \
-      E3FF2839C048B25C084DEBE9B26995E310250568
-
-#