remove the unnecessary fmt.Scanln command

[mhmmdd]

Fixes #59 in the way suggested here https://github.com/exercism/go-test-runner/issues/59#issuecomment-999874166

Without this code test runner has been tested following scenarios and it seems perfectly fine.

1. Running the test runner on Windows/Linux

$ go run . testrunner/testdata/practice/passing test

2. Running the test runner in the container by passing in the slug name

# Build the local docker image
$ docker build --rm -t exercism/test-runner .

# Run the test runner and see the results in the test folder
$ docker run --network none -v $(pwd)/testrunner/testdata/practice/gigasecond:/solution -v $(pwd)/test:/test exercism/test-runner gigasecond /solution /test

3. Running the test runner in the container by using attached mode

# Build the local docker image
$ docker build --rm -t exercism/test-runner .

# Run a container with attachmed mode
$ docker run --entrypoint /bin/sh --rm --name exercism-go-test-runner -d --network none -v $(pwd):/opt/test-runner -v $(pwd)/test:/test -it exercism/test-runner

# Access the container
$ docker exec -it --user appuser $(docker ps -q --filter name=exercism-go-test-runner) /bin/sh

# Run the test runner inside the container
$ go run . testrunner/testdata/practice/passing /test

[junedev]

@mhmmdd FYI: We need approval from one of the two admins to merge this change. Because of the holiday season, it can take a while until one of them has time to approve this.