Revert "Manually install go 1.16 until github actions updates image"

This reverts commit bf7f957af2.

We still have to manually install it for now but we don't have to fuck around
with env vars anymore. github actions still defaults to go 1.15 [1]. Whatever.

[1]
```
ls -lisah $(which go)
108022 0 lrwxrwxrwx 1 root root 42 Mar 18 22:15 /usr/bin/go ->
/opt/hostedtoolcache/go/1.15.10/x64/bin/go
```

.github/workflows/ci.yml

@@ -14,14 +14,14 @@ jobs:
         git config user.name "GitHub Action"
         git config user.email "action@github.com"
         git log -1 --format="%H"
+    - name: go
+      run: sudo snap install go --classic
     - name: test
-      run: |
-        sudo snap install go --edge --classic
-        GOROOT=/snap/go/current make test
+      run: make test
     - name: gh-pages
       run: |
         git checkout --orphan gh-pages && git reset
-        GOROOT=/snap/go/current make generate-gh-pages
+        make generate-gh-pages
         git add -f docs/ && git commit -m deploy
         git push -f origin gh-pages
     - name: notify