RFR: 8299865: Unnecessary NullPointerException catch in java.util.TimeZone#setDefaultZone

[Justin Lu]

In [JDK-4368016](https://bugs.openjdk.org/browse/JDK-4368016) **TimeZone.setDefaultZone()** was updated so that 

_TimeZone.java [will] not cause an NPE. If getSystemTimeZoneID()
can't determine the time zone from java.home and user.region properties,
it returns GMT._ 

This change updates the code to get rid of the no longer needed Try Catch

-------------

Commit messages:
 - Remove local variable javaHome
 - Indentation
 - Remove try catch block

Changes: https://git.openjdk.org/jdk/pull/11951/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11951&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299865
  Stats: 8 lines in 1 file changed: 0 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11951.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11951/head:pull/11951

PR: https://git.openjdk.org/jdk/pull/11951