Remove some unused code.

gyp is no longer needed on sys.path after
https://chromium-review.googlesource.com/c/chromium/src/+/1063611

Bug: 826218
Change-Id: I5ee268cab2f75b4fd6bddd62685f14dee4669626
Reviewed-on: https://chromium-review.googlesource.com/1199572Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588182}

build/vs_toolchain.py

@@ -17,9 +17,6 @@ from gn_helpers import ToGNString
 
 
 script_dir = os.path.dirname(os.path.realpath(__file__))
-chrome_src = os.path.abspath(os.path.join(script_dir, os.pardir))
-SRC_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-sys.path.insert(0, os.path.join(chrome_src, 'tools', 'gyp', 'pylib'))
 json_data_file = os.path.join(script_dir, 'win_toolchain.json')