RFR: Fix deprecation warnings coming from JDK 16

Fri Jul 2 15:42:08 UTC 2021

This PR fixes compilation warnings that fail builds during compilation because of -Werror flag.
The issues with compilation appear on JDK 16. Warnings that were fixed:
- warning: [missing-explicit-ctor] class JTRegModuleHelper in exported package java.lang declares no explicit constructors, thereby exposing a default constructor to clients of module java.base
- SimpleReporter.java:*: warning: [removal] Integer(int) in Integer has been deprecated and marked for removal 

After the changes build passes.

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Commit messages:
 - Fix deprecation warnings coming from JDK 16

Changes: https://git.openjdk.java.net/jtreg/pull/15/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=15&range=00
  Stats: 17 lines in 2 files changed: 5 ins; 0 del; 12 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/15.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/15/head:pull/15

PR: https://git.openjdk.java.net/jtreg/pull/15