Slim down project upgrade output

[Dhghomon]

Resolves #1190

First took a look at getting the multiline-into-single line issue solved through the attributes that clap (Rust's command-line parser) has, but on second look there's no info there that isn't contained in the options below, except for one example of an argument when moving to a specific version. So outright deleting this legacy comment seems best.

(As always, feel free to suggest a rewording)

Changes the output from this:

Upgrade EdgeDB instance used for current project

This command has two modes of operation.

Upgrade instance to version specified in `edgedb.toml`:

project upgrade

Update `edgedb.toml` to new version and upgrade the instance:

project upgrade --to-latest project upgrade --to-version=1-beta2 project upgrade --to-nightly

In all cases your data is preserved and converted using dump/restore mechanism. May fail if lower
version is specified (e.g. if upgrading from nightly to stable).

Usage: edgedb.exe project upgrade [OPTIONS]

Options:
      --project-dir <PROJECT_DIR>
          Explicitly set a root directory for the project

      --to-latest
          Upgrade specified instance to latest version

      --to-version <TO_VERSION>
          Upgrade specified instance to a specified version

      --to-nightly
          Upgrade specified instance to latest nightly version

      --to-testing
          Upgrade specified instance to latest testing version

      --to-channel <TO_CHANNEL>
          Upgrade specified instance to the specified channel

          [possible values: stable, testing, nightly]

  -v, --verbose
          Verbose output

      --force
          Force upgrade process even if there is no new version

      --non-interactive
          Do not ask questions, assume user wants to upgrade instance

  -h, --help
          Print help (see a summary with '-h')

to this

Upgrade EdgeDB instance used for current project

Data is preserved using a dump/restore mechanism.

Upgrades to version specified in `edgedb.toml` unless other options specified.

Note: May fail if lower version is specified (e.g. moving from nightly to stable).

Usage: edgedb.exe project upgrade [OPTIONS]

Options:
      --project-dir <PROJECT_DIR>
          Explicitly set a root directory for the project

      --to-latest
          Upgrade specified instance to latest version

      --to-version <TO_VERSION>
          Upgrade specified instance to a specified version.

          e.g. --to-version=4.0-beta.1

      --to-nightly
          Upgrade specified instance to latest nightly version

      --to-testing
          Upgrade specified instance to latest testing version

      --to-channel <TO_CHANNEL>
          Upgrade specified instance to the specified channel

          [possible values: stable, testing, nightly]

  -v, --verbose
          Verbose output

      --force
          Force upgrade process even if there is no new version

      --non-interactive
          Do not ask questions, assume user wants to upgrade instance

  -h, --help
          Print help (see a summary with '-h')

[raddevon]

Looks good! I provided one tiny suggestion.