[nomaster] Revert "Fixes SI-6521, overrides Range#head to be faster"

This reverts commit a557a97.

This is necessary to maintain binary compatibility with 2.10.0.

Mima says:

    matchName="scala.collection.immutable.Range.head"
    problemName=IncompatibleResultTypeProblem

The bridge method appeared because result is now Int, whereas
the super-method's result type erases to Object

Author: adriaanm

bincompat-forward.whitelist.conf

@@ -21,10 +21,10 @@ filter {
             problemName=MissingMethodProblem
         },
         # TODO: revert a557a97360: bridge method appeared because result is now Int but the super-method's result type erases to Object
-        {
-            matchName="scala.collection.immutable.Range.head"
-            problemName=IncompatibleResultTypeProblem
-        },
+        # {
+        #     matchName="scala.collection.immutable.Range.head"
+        #     problemName=IncompatibleResultTypeProblem
+        # },
         # TODO: revert 0b92073a38 2aa66bec86: SI-4664 [Make scala.util.Random Serializable] Add test case
         {
             matchName="scala.util.Random"

src/library/scala/collection/immutable/Range.scala

@@ -77,7 +77,6 @@ extends scala.collection.AbstractSeq[Int]
   final val terminalElement = start + numRangeElements * step
 
   override def last = if (isEmpty) Nil.last else lastElement
-  override def head = if (isEmpty) Nil.head else start
 
   override def min[A1 >: Int](implicit ord: Ordering[A1]): Int =
     if (ord eq Ordering.Int) {