[wasm] Remove dead wasm_execution_time counter

The counter is dead since August 2017 (https://crrev.com/c/633703).
The corresponding chromium histogram is removed in
https://crrev.com/c/1514812.

R=titzer@chromium.org

Bug: v8:8975
Change-Id: I6fa457018deb25cfd36d7de660fcfe996902c811
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1514737Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60185}

src/counters.h

@@ -1297,8 +1297,6 @@ class RuntimeCallTimerScope {
   HT(asm_wasm_translation_time, V8.AsmWasmTranslationMicroSeconds, 1000000,    \
      MICROSECOND)                                                              \
   HT(wasm_lazy_compilation_time, V8.WasmLazyCompilationMicroSeconds, 1000000,  \
-     MICROSECOND)                                                              \
-  HT(wasm_execution_time, V8.WasmExecutionTimeMicroSeconds, 10000000,          \
      MICROSECOND)
 
 #define TIMED_HISTOGRAM_LIST(HT)                                               \