RFR: 8308091: Remove unused iRegIHeapbase() matching operand [v2]

[Xiaolin Zheng]

> The `iRegIHeapbase()` matching operand has no usage on both AArch64 and RISC-V platforms after [JDK-8242449](https://bugs.openjdk.org/browse/JDK-8242449) and [JDK-8306667](https://bugs.openjdk.org/browse/JDK-8306667), respectively. As the following-up action discussed in the code review process of [JDK-8306667](https://bugs.openjdk.org/browse/JDK-8306667) (#13577), this is a small cleanup for the `iRegIHeapbase()` matching operand.
> 
> Passed fastdebug/release build on both AArch64/RISC-V platforms.
> 
> Thanks,
> Xiaolin

Xiaolin Zheng has updated the pull request incrementally with one additional commit since the last revision:

  Further cleanups

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13983/files
  - new: https://git.openjdk.org/jdk/pull/13983/files/41d36c4e..c26b96c9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13983&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13983&range=00-01

  Stats: 18 lines in 2 files changed: 0 ins; 10 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/13983.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13983/head:pull/13983

PR: https://git.openjdk.org/jdk/pull/13983