Remove old deprecated items in Spark 3

There are many deprecated methods and classes in Spark. They can be removed in Spark 3, and for those that have been deprecated a long time (i.e. since Spark <= 2.0), we should probably do so. This addresses most of these cases, the easiest ones, those that are easy to remove and are old:

• Remove some AccumulableInfo .apply() methods
• Remove non-label-specific multiclass precision/recall/fScore in favor of accuracy
• Remove toDegrees/toRadians in favor of degrees/radians (SparkR: only deprecated)
• Remove approxCountDistinct in favor of approx_count_distinct (SparkR: only deprecated)
• Remove unused Python StorageLevel constants
• Remove unused multiclass option in libsvm parsing
• Remove references to deprecated spark configs like spark.yarn.am.port
• Remove TaskContext.isRunningLocally
• Remove ShuffleMetrics.shuffle* methods
• Remove BaseReadWrite.context in favor of session
• Remove Column.Unable to render embedded object: File (== in favor of =) not found.=
• Remove Dataset.explode
• Remove Dataset.registerTempTable
• Remove SQLContext.getOrCreate, setActive, clearActive, constructors

Not touched yet:

• everything else in MLLib
• HiveContext
• Anything deprecated more recently than 2.0.0, generally