[tools] Make v8_linux64_header_includes_dbg non-experimental

TBR=machenbach@chromium.org

No-Try: true
No-Tree-Checks: true
Bug: v8:7966
Change-Id: I354622e8b0fca7df957c7484cedeef728cfa3f57
Reviewed-on: https://chromium-review.googlesource.com/1148322Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54640}

infra/config/cq.cfg

@@ -36,10 +36,7 @@ verifiers {
         triggered_by: "v8_linux64_dbg_ng"
       }
       builders { name: "v8_linux64_gcc_compile_dbg" }
-      builders {
-        name: "v8_linux64_header_includes_dbg"
-        experiment_percentage: 100
-      }
+      builders { name: "v8_linux64_header_includes_dbg" }
       builders { name: "v8_linux64_jumbo_compile_rel" }
       builders { name: "v8_linux64_rel_ng" }
       builders {