RFR: 8348687: [BACKOUT] C2: Non-fluid StringBuilder pattern bails out in OptoStringConcat

[Theo Weidmann]

Backs out the changes introduced in [JDK-8341696](https://bugs.openjdk.org/browse/JDK-8341696) as they cause a bug in a benchmark.

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

Commit messages:
 - Revert "8341696: C2: Non-fluid StringBuilder pattern bails out in OptoStringConcat"

Changes: https://git.openjdk.org/jdk/pull/23348/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23348&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348687
  Stats: 358 lines in 4 files changed: 43 ins; 291 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/23348.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23348/head:pull/23348

PR: https://git.openjdk.org/jdk/pull/23348