[Enhancement] Clean pillow version check (open-mmlab#1691)

* Clean pillow version check

* modify test_mim

Author: xiexinch

.github/workflows/build.yml

@@ -53,9 +53,6 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: Upgrade pip
         run: pip install pip --upgrade
-      - name: Install Pillow
-        run: pip install Pillow==6.2.2
-        if: ${{matrix.torchvision == '0.4.2'}}
       - name: Install PyTorch
         run: pip install torch==${{matrix.torch}}+cpu torchvision==${{matrix.torchvision}}+cpu -f https://download.pytorch.org/whl/torch_stable.html
       - name: Install MMCV

.github/workflows/test_mim.yml

@@ -34,9 +34,6 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: Upgrade pip
         run: pip install pip --upgrade
-      - name: Install Pillow
-        run: pip install Pillow==6.2.2
-        if: ${{matrix.torchvision == '0.4.2'}}
       - name: Install PyTorch
         run: pip install torch==${{matrix.torch}}+cpu torchvision==${{matrix.torchvision}}+cpu -f https://download.pytorch.org/whl/torch_stable.html
       - name: Install openmim