[SPARK-14617] Remove deprecated APIs in TaskMetrics

[rxin]

What changes were proposed in this pull request?

This patch removes some of the deprecated APIs in TaskMetrics. This is part of my bigger effort to simplify accumulators and task metrics.

How was this patch tested?

N/A - only removals

[SparkQA]

Test build #55770 has finished for PR 12375 at commit 98c8020.

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

[SparkQA]

Test build #55780 has finished for PR 12375 at commit f9aebc0.

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

[SparkQA]

Test build #2786 has finished for PR 12375 at commit f9aebc0.

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

[SparkQA]

Test build #2787 has finished for PR 12375 at commit f9aebc0.

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

[rxin]

cc @andrewor14

[SparkQA]

Test build #55807 has finished for PR 12375 at commit b970609.

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

[andrewor14]

Merging into master.