CI: Do not change the system gcc version to 10

Because the Serenity tooling autodetects the presence of gcc 10
it is no longer necessary to change the system gcc version to 10.

.github/workflows/cmake.yml

@@ -48,9 +48,6 @@ jobs:
         sudo add-apt-repository ppa:canonical-server/server-backports
         sudo apt-get update
         sudo apt-get install libmpfr-dev libmpc-dev ninja-build e2fsprogs qemu-utils qemu-system-i386 ccache
-    - name: Use GCC 10 instead
-      run: sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 100 --slave /usr/bin/g++ g++ /usr/bin/g++-10
-
     - name: Install JS dependencies
       run: sudo npm install -g prettier@2.2.1
     - name: Install Python dependencies