[SPARK-16581][SPARKR] Fix JVM API tests in SparkR

## What changes were proposed in this pull request?

Remove cleanup.jobj test. Use JVM wrapper API for other test cases.

## How was this patch tested?

Run R unit tests with testthat 1.0

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #14904 from shivaram/sparkr-jvm-tests-fix.