Revert "[turbofan] Temporarily disable future=>concurrent_inlining"

This reverts commit ce421122.

Reason for revert: https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20debug/27535

Original change's description:
> [turbofan] Temporarily disable future=>concurrent_inlining
> 
> ... in order to reset the benchmarks now that we are actually running
> in the background.
> 
> Bug: v8:7790
> Change-Id: Ifa811fbcc51eccef790e6215d330f8b45c31a492
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1801836
> Reviewed-by: Georg Neis <neis@chromium.org>
> Commit-Queue: Georg Neis <neis@chromium.org>
> Auto-Submit: Maya Lekova <mslekova@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63741}

TBR=neis@chromium.org,mslekova@chromium.org

Change-Id: Ia36bc6a600c78b370a29964fabd215f853e048f9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7790
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1803234Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63742}

src/flags/flag-definitions.h

@@ -484,6 +484,7 @@ DEFINE_BOOL(block_concurrent_recompilation, false,
             "block queued jobs until released")
 DEFINE_BOOL(concurrent_inlining, false,
             "run optimizing compiler's inlining phase on a separate thread")
+DEFINE_IMPLICATION(future, concurrent_inlining)
 DEFINE_BOOL(trace_heap_broker_verbose, false,
             "trace the heap broker verbosely (all reports)")
 DEFINE_BOOL(trace_heap_broker, false,