[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.

R/pkg/inst/tests/testthat/test_jvm_api.R

@@ -20,24 +20,17 @@ context("JVM API")
 sparkSession <- sparkR.session(enableHiveSupport = FALSE)
 
 test_that("Create and call methods on object", {
-  jarr <- newJObject("java.util.ArrayList")
+  jarr <- sparkR.newJObject("java.util.ArrayList")
   # Add an element to the array
-  callJMethod(jarr, "add", 1L)
+  sparkR.callJMethod(jarr, "add", 1L)
   # Check if get returns the same element
-  expect_equal(callJMethod(jarr, "get", 0L), 1L)
+  expect_equal(sparkR.callJMethod(jarr, "get", 0L), 1L)
 })
 
 test_that("Call static methods", {
   # Convert a boolean to a string
-  strTrue <- callJStatic("java.lang.String", "valueOf", TRUE)
+  strTrue <- sparkR.callJStatic("java.lang.String", "valueOf", TRUE)
   expect_equal(strTrue, "true")
 })
 
-test_that("Manually garbage collect objects", {
-  jarr <- newJObject("java.util.ArrayList")
-  cleanup.jobj(jarr)
-  # Using a jobj after GC should throw an error
-  expect_error(print(jarr), "Error in invokeJava.*")
-})
-
 sparkR.session.stop()