SI-8251 Remove ListBuffer.readOnly as deprecated

src/library/scala/collection/mutable/BufferLike.scala

@@ -211,13 +211,6 @@ trait BufferLike[A, +This <: BufferLike[A, This] with Buffer[A]]
    */
   override def stringPrefix: String = "Buffer"
 
-  /** Returns the current evolving(!) state of this buffer as a read-only sequence.
-   *
-   *  @return  A sequence that forwards to this buffer for all its operations.
-   */
-  @deprecated("The returned sequence changes as this buffer is mutated. For an immutable copy, use, e.g., toList.", "2.11.0")
-  def readOnly: scala.collection.Seq[A] = toSeq
-
   /** Creates a new collection containing both the elements of this collection and the provided
    *  traversable object.
    *

src/library/scala/collection/mutable/BufferProxy.scala

@@ -43,8 +43,6 @@ trait BufferProxy[A] extends Buffer[A] with Proxy {
    */
   def +=(elem: A): this.type = { self.+=(elem); this }
 
-  override def readOnly = self.readOnly
-
   /** Appends a number of elements provided by a traversable object.
    *
    *  @param xs   the traversable object.

src/library/scala/collection/mutable/ListBuffer.scala

@@ -408,9 +408,6 @@ final class ListBuffer[A]
       }
   }
 
-  @deprecated("The result of this method will change along with this buffer, which is often not what's expected.", "2.11.0")
-  override def readOnly: List[A] = start
-
   // Private methods
 
   /** Copy contents of this buffer */
@@ -426,7 +423,7 @@ final class ListBuffer[A]
   }
 
   override def equals(that: Any): Boolean = that match {
-    case that: ListBuffer[_] => this.readOnly equals that.readOnly
+    case that: ListBuffer[_] => this.start equals that.start
     case _                   => super.equals(that)
   }