remove gsl dependency from CI

Author: m-murphy

.github/workflows/pkgdown.yaml

@@ -16,9 +16,6 @@ jobs:
 
       - uses: r-lib/actions/setup-pandoc@master
 
-      - name: Install GSL
-        run: brew install gsl
-
       - name: Query dependencies
         run: |
           install.packages('remotes')