Revert of [Interpreter] Rename GetCountOperand to GetRegisterCountOperand. (patchset #1 id:20001 of https://codereview.chromium.org/1691433002/ )

Reason for revert:
[Sheriff] Breaks the tree:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20builder/builds/13892

Blamelists are wrong because of overloaded master. The trybots on this CL might have been outdated by the time of commit... Please rebase and retry.

Original issue's description:
> [Interpreter] Rename GetCountOperand to GetRegisterCountOperand.
>
> Apparently, this BytecodeArrayIterator method was missed during the
> previous refactor. No other (collateral) change was done.
>
> BUG=v8:4280
> LOG=N
>
> Committed: https://crrev.com/3781ca79f5c48b55d7f0bf6df370ec11515a1466
> Cr-Commit-Position: refs/heads/master@{#33897}

TBR=oth@chromium.org,rmcilroy@chromium.org,mstarzinger@chromium.org,ssanfilippo@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4280

Review URL: https://codereview.chromium.org/1690963002

Cr-Commit-Position: refs/heads/master@{#33900}