[breaking] Removed redundant and useless commands from gRPC API

[cmaglie]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

• What kind of change does this PR introduce?
  Removes the gRPC commands:

  rpc UpdateCoreLibrariesIndex(UpdateCoreLibrariesIndexRequest) returns (stream UpdateCoreLibrariesIndexResponse) {}
  rpc Outdated(OutdatedRequest) returns (OutdatedResponse) {}
  rpc Upgrade(UpgradeRequest) returns (stream UpgradeResponse) {}

• What is the current behavior?
  The code for these cli commands (execution, rendering, error reporting...) is duplicated from 2 to 3 times.

• What is the new behavior?
  Removed all code duplication.

• Does this PR introduce a breaking change, and is
  titled accordingly?
  Yes, the gRPC API calls described above have been removed.