RFR: 8265418: Clean-up redundant null-checks of Class.getPackageName() [v3]

[Сергей Цыпанов]

> As discussed in https://github.com/openjdk/jdk/pull/3464 we can clean-up null-checks remaining after [8142968](https://bugs.openjdk.java.net/browse/JDK-8142968) as Class.getPackageName() never returns null.

Сергей Цыпанов has updated the pull request incrementally with one additional commit since the last revision:

  8265418: Compare package names with == instead of equals()

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3571/files
  - new: https://git.openjdk.java.net/jdk/pull/3571/files/7d52a13d..dc91091b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3571&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3571&range=01-02

  Stats: 7 lines in 6 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3571.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3571/head:pull/3571

PR: https://git.openjdk.java.net/jdk/pull/3571