RFR: 8364570: Remove LockingMode related code from riscv64 [v2]

[Fredrik Bredberg]

> Since the integration of [JDK-8359437](https://bugs.openjdk.org/browse/JDK-8359437) the `LockingMode` flag can no longer be set by the user, instead it's declared as `const int LockingMode = LM_LIGHTWEIGHT;`. This means that we can now safely remove all `LockingMode` related code from all platforms.
> 
> This PR removes `LockingMode` related code from the **riscv64** platform.
> 
> When all the `LockingMode` code has been removed from all platforms, we can go on and remove it from shared (non-platform specific) files as well. And finally remove the `LockingMode` variable itself.

Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:

  Update one after review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26658/files
  - new: https://git.openjdk.org/jdk/pull/26658/files/ea85a52d..a32ae39e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26658&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26658&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26658.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26658/head:pull/26658

PR: https://git.openjdk.org/jdk/pull/26658