[2.x] refactor: Remove old sbt 0.13 shell syntax

[eed3si9n]

Fixes #7696

Problem

sbt 1.x introduced the slash syntax midway, so it kept the old a/test:console::scalacOptions syntax, which hopefully aren't in any more. sbt 1.x has been displaying deprecation warning on this.

sbt:sbtRoot> mainProj/test:console::scalacOptions
[warn] sbt 0.13 shell syntax is deprecated; use slash syntax instead: mainProj / Test / console / scalacOption

Solution

This removes the support from the shell parser.

[SethTisue]

amazing 👏