Update CircleCI image

We shouldn't need all those custom PPAs anymore

.circleci/config.yml

@@ -4,7 +4,7 @@ orbs:
 jobs:
   build:
     machine:
-      image: 'ubuntu-1604:202004-01'
+      image: 'ubuntu-2004:202010-01'
     steps:
       - git-shallow-clone/checkout
       - run:
@@ -15,24 +15,11 @@ jobs:
       - run:
           name: Install dependencies
           command: |
-            # keys
-            wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | sudo apt-key add -
-            wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
-            
-            # repos
-            sudo apt-add-repository 'deb https://apt.kitware.com/ubuntu/ xenial main'
-            sudo apt-add-repository 'deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
-            sudo add-apt-repository ppa:deadsnakes/ppa
-            
             sudo dpkg --add-architecture i386
             
             sudo apt-get update
-            sudo apt-get upgrade -y cmake
-            sudo apt-get install --no-install-recommends -y devscripts equivs debhelper libdistro-info-perl python3.8 clang-9 libfreetype6-dev:i386
+            sudo apt-get install --no-install-recommends -y devscripts equivs debhelper libdistro-info-perl libfreetype6-dev:i386
             sudo mk-build-deps -i -r -t "apt-get --no-install-recommends -y" debian/control
-            
-            sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.8 1
-            sudo update-alternatives --auto python3
       - run:
           name: Build DSCs
           no_output_timeout: 30m