RFR: 8286560: Remove user parameter from jdk.internal.perf.Perf.attach()

[Ioi Lam]

The API `jdk.internal.perf.Perf.::attach(String user, int lvmid)` is never used. It should be removed, and all the handling of a specified user name should be removed.

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

Commit messages:
 - more cleanup
 - 8286560: Remove user parameter from jdk.internal.perf.Perf.attach()

Changes: https://git.openjdk.java.net/jdk/pull/8669/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8669&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286560
  Stats: 120 lines in 5 files changed: 2 ins; 95 del; 23 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8669.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8669/head:pull/8669

PR: https://git.openjdk.java.net/jdk/pull/8669