RFR: 8286441: Remove mode parameter from jdk.internal.perf.Perf.attach()

[Ioi Lam]

The `mode` parameter for ` jdk.internal.perf.Perf.attach()` has never supported the value `"rw"` since the source code was imported to the openjdk repo more than 15 years ago. In fact HotSpot throws `IllegalArgumentException` when such a mode is specified.

It's unlikely such a mode will be required for future enhancements. Support for `"rw"` is removed. The "mode" parameter is also removed, since now `"r"` is the only supported mode.

I also cleaned up related code in the JDK and HotSpot.

Testing:
- Passed tiers 1 and 2
- Tiers 3, 4, 5 are in progress

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Commit messages:
 - 8286441: Remove mode parameter from jdk.internal.perf.Perf.attach()

Changes: https://git.openjdk.java.net/jdk/pull/8622/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8622&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286441
  Stats: 193 lines in 15 files changed: 0 ins; 144 del; 49 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8622.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8622/head:pull/8622

PR: https://git.openjdk.java.net/jdk/pull/8622