chore(dependabot): remove tsmorph settings

tsmorph was removed in #508, so we
can remove the associated dependabot configuration.

Author: ericcrosson-bitgo

.github/dependabot.yml

@@ -30,8 +30,6 @@ updates:
         update-types: ['version-update:semver-patch']
       - dependency-name: io-ts
         versions: ['2.x']
-      - dependency-name: ts-morph
-        versions: ['>=16']
       - dependency-name: typescript
         versions: ['>4.8']
       - dependency-name: whatwg-url