Rename install.sh to prerequisites.sh

This way, GAP's BuildPackages.sh script will automatically execute it,
meaning that cddlib will end up being available for more users than
without this.

The GH actions CI scripts also use this, so no need for libcdd-dev
anymore.

Author: fingolfin

.github/workflows/CI.yml

@@ -31,10 +31,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
-      - name: 'Install additional dependencies'
-        run: |
-          sudo apt-get update
-          sudo apt-get install libcdd-dev
       - uses: gap-actions/setup-gap@v2
         with:
           GAPBRANCH: ${{ matrix.gap-branch }}
@@ -50,10 +46,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
-      - name: 'Install additional dependencies'
-        run: |
-          sudo apt-get update
-          sudo apt-get install libcdd-dev
       - uses: gap-actions/setup-gap@v2
       - uses: gap-actions/build-pkg-docs@v1
         with: