[wasm] Fix duplicated tests for float to I64 tests

Fixes float to I64 tests to not have duplicated tests.

Also changes the use of macro REQUIRE to only be needed when an opcode
(i.e. operation) is not supported on some architecture.

Bug: v8:7226
Change-Id: I6c18602bd836469077808c0b3c93732af7c8f0d8
Reviewed-on: https://chromium-review.googlesource.com/895408
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51097}