RFR: 8280414: Memory leak in DefaultProxySelector

[Daniel Jeliński]

We were leaking the list returned by `createProxyList`. Verified that the leak is no longer present with this patch. Also removed a few unused variables.

Reported by clang-tidy.

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Commit messages:
 - Fix memory leak

Changes: https://git.openjdk.java.net/jdk/pull/7172/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7172&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280414
  Stats: 11 lines in 1 file changed: 1 ins; 3 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7172.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7172/head:pull/7172

PR: https://git.openjdk.java.net/jdk/pull/7172