RFR: 8304034: Remove redundant and meaningless comments in opto

[Yi Yang]

Please help review this trivial change to remove redundant and meaningless comments in `hotspot/share/opto` directory.

They are either
1. Repeat the function name that the function they comment for.
2. Makes no sense, e.g. `//----Idealize----` 

And I think original CC-style code (`if( test )`,`call( arg )`) can be formatted in one go, instead of formatting the near code when someone touches them. But this may form a big patch, and it confuses code blame, so I left this work until we reach a consensus.

Thanks!

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Commit messages:
 - remove useless comments

Changes: https://git.openjdk.org/jdk/pull/12995/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12995&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304034
  Stats: 2135 lines in 97 files changed: 0 ins; 2135 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12995.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12995/head:pull/12995

PR: https://git.openjdk.org/jdk/pull/12995