Scala 3 book: streamline getting-started instructions a bit (#2293)

Author: SethTisue

_config.yml

@@ -18,7 +18,6 @@ keywords:
 scala-version: 2.13.8
 scala-212-version: 2.12.15
 scala-3-version: 3.1.0
-scala-3-plugin-version: 0.5.1
 
 collections:
   style:

_overviews/scala3-book/tools-sbt.md

@@ -47,7 +47,7 @@ Create a file named _build.properties_ in the directory `project`, with
 the following content:
 
 ```text
-sbt.version=1.5.4
+sbt.version=1.6.1
 ```
 
 Then create a file named _build.sbt_ in the project root directory that contains this line:
@@ -101,9 +101,6 @@ These are working directories that sbt uses.
 
 As you can see, creating and running a little Scala project with sbt takes just a few simple steps.
 
-> For sbt version < 1.5.0, it is required to have the following line in a *project/plugins.sbt* file: `addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "{{ site.scala-3-plugin-version }}")`
-
-
 ### Using sbt with larger projects
 
 For a little project, that’s all that sbt requires to run.