RFR: 8293050: RISC-V: Remove redundant non-null assertions about macro-assembler [v2]

[Fei Yang]

> There are some non-null assertions about macro-assembler in riscv-specific code. Most of them are there to make some internal code-check tools happy. We should remove those redundant assertions to make the code clean.
> 
> Tested with tier1 hotspot on linux-riscv64 unmatched.

Fei Yang has updated the pull request incrementally with one additional commit since the last revision:

  Fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10079/files
  - new: https://git.openjdk.org/jdk/pull/10079/files/126780fb..3547131e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10079&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10079&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10079.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10079/head:pull/10079

PR: https://git.openjdk.org/jdk/pull/10079