CI: Only install packages not already present

The GitHub runners have most of the required packages installed already.
Only install the 3 extra that we need for ct-ng.

Signed-off-by: Chris Packham <judge.packham@gmail.com>

.github/workflows/continuous-integration-workflow.yml

@@ -22,10 +22,7 @@ jobs:
         uses: actions/checkout@v2
       - name: "prereq"
         run: |
-          sudo apt-get install -y gcc g++ gperf bison flex texinfo help2man \
-                                  make libncurses5-dev python3-dev autoconf \
-                                  automake libtool libtool-bin gawk wget bzip2 \
-                                  xz-utils unzip patch libstdc++6 rsync
+          sudo apt-get install -y gperf help2man libtool-bin
       - name: "build ct-ng"
         run: |
           ./bootstrap