delete useless var “j”

the var “j” defined in "var j = 0" is useless for “def compress”

Author: Souljoy Zhuo <zhuoshoujie@126.com>

Closes #16676 from xiaoyesoso/patch-1.

mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala

@@ -1038,14 +1038,12 @@ object ALS extends DefaultParamsReadable[ALS] with Logging {
       uniqueSrcIdsBuilder += preSrcId
       var curCount = 1
       var i = 1
-      var j = 0
       while (i < sz) {
         val srcId = srcIds(i)
         if (srcId != preSrcId) {
           uniqueSrcIdsBuilder += srcId
           dstCountsBuilder += curCount
           preSrcId = srcId
-          j += 1
           curCount = 0
         }
         curCount += 1