[turbofan] Remove out-of-line defn of constexpr vars

It's deprecated in C++17 and not needed (it was needed for
static const, but not for constexpr)

Bug: chromium:1274247
Change-Id: If92d7b6300493cb186ff2ade8f6b6a4820d5a264
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3306429
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78149}

src/compiler/js-heap-broker.cc

@@ -30,11 +30,6 @@ namespace compiler {
 
 #define TRACE(broker, x) TRACE_BROKER(broker, x)
 
-// These definitions are here in order to please the linker, which in debug mode
-// sometimes requires static constants to be defined in .cc files.
-const uint32_t JSHeapBroker::kMinimalRefsBucketCount;
-const uint32_t JSHeapBroker::kInitialRefsBucketCount;
-
 void JSHeapBroker::IncrementTracingIndentation() { ++trace_indentation_; }
 
 void JSHeapBroker::DecrementTracingIndentation() { --trace_indentation_; }