[Minor][SparkR] Minor refactor and removes redundancy related to cleanClosure.

[hlin09]

1. Only use cleanClosure in creation of RRDDs. Normally, user and developer do not need to call cleanClosure in their function definition.
2. Removes redundant code (e.g. unnecessary wrapper functions) related to cleanClosure.

[concretevitamin]

Jenkins, test this please.

[concretevitamin]

Hey @pwendell I can't seem to summon Jenkins now :(

[shivaram]

Jenkins, test this please

[SparkQA]

Test build #30200 has finished for PR 5495 at commit 74ec303.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.
• This patch does not change any dependencies.

[shivaram]

LGTM. @concretevitamin did you have any comments ?

[concretevitamin]

LGTM