parallel_emerge: drop python3.6 path

Since python is python3.6 by default now, no need to hardcode this.

BUG=chromium:991683
TEST=CQ passes

Change-Id: I428b8bb0f01097fa9383d83d32478b1b9485c195
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1962719
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/parallel_emerge.py b/scripts/parallel_emerge.py
index 6d4340a..2d96e0b 100644
--- a/scripts/parallel_emerge.py
+++ b/scripts/parallel_emerge.py
@@ -148,6 +148,4 @@
   emerge_args.append('--jobs=%s' % parsed_args['jobs'])
   emerge_args.append('--rebuild-exclude=chromeos-base/chromeos-chrome')
 
-  # TODO(cjmcdonald): Change the exec target back to just 'emerge' once
-  #                   python3 is the default in the SDK.
-  os.execvp('/usr/lib64/python-exec/python3.6/emerge', ['emerge'] + emerge_args)
+  os.execvp('emerge', ['emerge'] + emerge_args)