Remove `BTab` from `GlTab`

BootstrapVue props we should support

• disabled
• id
• lazy
• title
• title-item-class
• title-link-attributes
• title-link-class

BootstrapVue props we should consider not supporting

https://gitlab-org.gitlab.io/frontend/bootstrapvue-component-usage-breakdown/components.json can be used as a starting point to see if the prop is used, but should not be considered an exhaustive list (it does not check https://gitlab.com/gitlab-org/customers-gitlab-com/ or Switchboard, please do this manually). We should weigh the pros and cons of supporting each prop individually.

• active
• button-id
• no-body
• tag

BootstrapVue slots we should support

• default
• title

BootstrapVue events we should support

• click