Don't use npm update before publication

In our projects we use `npm update` to resolve latest versions for
prerelease packages from `@keep-network` scope that the current project
depends on. In case of `sortition-pools` there are no dependencies to any
contracts so we don't need to use `npm update`.

What plain `npm update` did was updating all the packages we defined in
dependencies that could cause problems as we were testing agains
specific versions locked in package-lock and also CI executed it's tests
agains them but here at the very last step before package publication we
updated locked versions. If we need to update contracts dependencies in
prerelease cycle we should specify which packages we want to update,
e.g. `npm update @keep-network/sortition-pools`.

.github/workflows/npm.yml

@@ -66,9 +66,6 @@ jobs:
           # Consider including commit id? Would be +<commit id>.
           npm version prerelease --preid=$preid --no-git-tag-version
 
-          # Fix resolved dependency versions.
-          npm update
-
       - name: Publish package
         run: npm publish --access public
         env: