Remove use of explicit pip cache.

We use setup-python to install the python we use, which has inbuilt
caching of python dependencies.

https://github.com/actions/setup-python#caching-packages-dependencies

.github/workflows/integration_tests.yml

@@ -65,14 +65,6 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.8
-      - name: Cache pip
-        uses: actions/cache@v2
-        with:
-          path: ~/.cache/pip
-          key: ${{ runner.os }}-pip
-          restore-keys: |
-            ${{ runner.os }}-pip-
-            ${{ runner.os }}-
       - uses: actions/cache@v2
         with:
           path: |

.github/workflows/sanity_test.yml

@@ -27,14 +27,6 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.8
-      - name: Cache pip
-        uses: actions/cache@v2
-        with:
-          path: ~/.cache/pip
-          key: ${{ runner.os }}-pip
-          restore-keys: |
-            ${{ runner.os }}-pip-
-            ${{ runner.os }}-
       - uses: actions/cache@v2
         with:
           path: |

.github/workflows/sync-from-external-sources.yml

@@ -15,14 +15,6 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.8
-      - name: Cache pip
-        uses: actions/cache@v2
-        with:
-          path: ~/.cache/pip
-          key: ${{ runner.os }}-pip
-          restore-keys: |
-            ${{ runner.os }}-pip-
-            ${{ runner.os }}-
       - name: Install Prerequisite dependencies
         run: |
           pip install BeautifulSoup4
@@ -49,14 +41,6 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.8
-      - name: Cache pip
-        uses: actions/cache@v2
-        with:
-          path: ~/.cache/pip
-          key: ${{ runner.os }}-pip
-          restore-keys: |
-            ${{ runner.os }}-pip-
-            ${{ runner.os }}-
       - name: Install Prerequisite dependencies
         run: |
           pip install requests