Revert of [inspector] migrate stepping related methods to debug-interface (patchset #3 id:40001 of https://chromiumcodereview.appspot.com/2423153002/ )

Reason for revert:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/10808

https://github.com/v8/v8/wiki/Blink-layout-tests

Original issue's description:
> [inspector] migrate stepping related methods to debug-interface
>
> * introduced DebugInterface::PrepareStep and DebugInterface::ClearStepping method.
> Inspector calls these methods only on pause and not interseted in calling this for not current break_id so we don't need to expose debug interface with break_id argument and can only check that current break_id is valid.
>
> BUG=chromium:652939,v8:5510
> R=yangguo@chromium.org,dgozman@chromium.org

TBR=yangguo@chromium.org,dgozman@chromium.org,kozyatinskiy@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:652939,v8:5510

Review-Url: https://chromiumcodereview.appspot.com/2441583002
Cr-Commit-Position: refs/heads/master@{#40455}