[SPARK-15250][SQL] Remove deprecated json API in DataFrameReader

[HyukjinKwon]

What changes were proposed in this pull request?

This PR removes the old json(path: String) API which is covered by the new json(paths: String*).

How was this patch tested?

Jenkins tests (existing tests should cover this)

[SparkQA]

Test build #58299 has finished for PR 13040 at commit 35db95f.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #58300 has finished for PR 13040 at commit 7c8ee6d.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #58303 has finished for PR 13040 at commit f9b123c.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #58304 has finished for PR 13040 at commit 5576054.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

(Sorry, I left a wrong comment referring unrelated PRs here and I removed that.)

[SparkQA]

Test build #58313 has finished for PR 13040 at commit d28b24d.

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

[HyukjinKwon]

cc @rxin

(I see doc tests and test in Python are still using SqlContext. Do you mind if I correct this for SparkSession in another PR?)

[rxin]

LGTM - merging in master/2.0.

[rxin]

Yes please submit another pr for those.

[tdas]

For future reference. Removing this method broke source compatibility in case as

Option(path).map(spark.read.json)  // does not compile, after this patch.

In this sort of shorthand of functions using 1 parameter, works only if the method signature has one parameter and does not work when the method has varargs.

[HyukjinKwon]

@tdas Thanks, I will keep in mind.