RFR: 8287766: Unnecessary Vector usage in LdapClient

[Andrey Turbanov]

In [JDK-8273098](https://bugs.openjdk.java.net/browse/JDK-8273098) I missed one place, where Vector could be replaced with ArrayList.
Usage of thread-safe collection `Vector` is unnecessary. It's recommended to use `ArrayList` if a thread-safe implementation is not needed.

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

Commit messages:
 - [PATCH] Unnecessary Vector usage in LdapClient

Changes: https://git.openjdk.java.net/jdk/pull/8940/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8940&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287766
  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8940.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8940/head:pull/8940

PR: https://git.openjdk.java.net/jdk/pull/8940