Remove Pontoon Intro project

[mathjazz]

Pontoon comes preinstalled with the Pontoon Intro project, which was used to demonstrate the in-context localization, which was removed in #2862. Hence, we should also remove the Pontoon Intro project.

References:

• pontoon/pontoon/base/migrations/0002_auto_20200322_1821.py

  Line 1336 in 44ab754

  def migration_0002_load_initial_data(apps, schema_editor):

• pontoon/docker/server_setup.sh

  Line 13 in 44ab754

  echo "Running migration of the pontoon-intro module"

• pontoon/pontoon/urls.py

  Line 56 in 44ab754

  path("intro/", RedirectView.as_view(url="/", permanent=True)),

• pontoon/pontoon/api/tests/test_schema.py

  Line 44 in 44ab754

  {"name": "Pontoon Intro"},

• https://github.com/mozilla/pontoon/blob/44ab754666d5e4b7b7c5407374d497c7f9bcc7f5/docs/dev/setup-virtualenv.rst#installation