[riscv-port-jdk11u:riscv-port] RFR: 8293050: RISC-V: Remove redundant non-null assertions about macro-assembler

[Fei Yang]

On Wed, 18 Sep 2024 01:15:31 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

> Please review this backport to riscv-port-jdk17u.
> Backport of [JDK-8293050](https://bugs.openjdk.org/browse/JDK-8293050).
> Applies not cleanly due to context difference, but it is easy to resolve them manually.
> 
> Testing:
> - Tier1 passed without new failure on unmatched (release).

Marked as reviewed by fyang (Lead).

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PR Review: https://git.openjdk.org/riscv-port-jdk11u/pull/32#pullrequestreview-2311516670