[SPARK-21970][Core] Fix Redundant Throws Declarations in Java Codebase

[original-brownbear]

What changes were proposed in this pull request?

1. Removing all redundant throws declarations from Java codebase.
2. Removing dead code made visible by this from ShuffleExternalSorter#closeAndGetSpills

How was this patch tested?

Build still passes.

[SparkQA]

Test build #3915 has finished for PR 19182 at commit 3181f69.

• This patch fails to generate documentation.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Some of these 'throws' clauses may not be removable because they cause callers that catch the checked exception to fail to compile.

Removing "throws Exception" in tests isn't obviously helpful, because it means the signature has to change any time the tested code happens to throw a new checked exception. There's no API problem as nothing invokes these methods directly.

Private non-test methods, maybe.

[original-brownbear]

@srowen makes perfect sense => rolled back all changes to tests + publicly exposed methods (those package private ones adjusted are on non-public classes).

[srowen]

This kind of thing looks like good cleanup if it compiles and passes MiMa

[SparkQA]

Test build #3916 has finished for PR 19182 at commit b69a20b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[original-brownbear]

@srowen looks like we're all green :)

[srowen]

Ah OK one more subtle thing @original-brownbear -- the code you see in org/apache/hive packages is, I believe, copied from Hive. Therefore it's probably best to leave it as-is because it makes it easier to update it if it hasn't varied at all from its source. Could you reverse those? otherwise looks OK.

[original-brownbear]

@srowen done, all changes to org.apache.hive.* reverted :)

[SparkQA]

Test build #3921 has finished for PR 19182 at commit cb8e80b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Merged to master