Moving get_landmines.py (build/ -> tools-webrtc/)

BUG=webrtc:7030
NOTRY=True

Review-Url: https://codereview.webrtc.org/2656553002
Cr-Commit-Position: refs/heads/master@{#16227}

DEPS

@@ -169,7 +169,7 @@ hooks = [
         'python',
         'src/build/landmines.py',
         '--landmine-scripts',
-        'src/webrtc/build/get_landmines.py',
+        'src/tools-webrtc/get_landmines.py',
         '--src-dir',
         'src',
     ],

tools-webrtc/get_landmines.py

@@ -16,7 +16,7 @@ import os
 import sys
 
 script_dir = os.path.dirname(os.path.realpath(__file__))
-checkout_root = os.path.abspath(os.path.join(script_dir, os.pardir, os.pardir))
+checkout_root = os.path.abspath(os.path.join(script_dir, os.pardir))
 sys.path.insert(0, os.path.join(checkout_root, 'build'))
 import landmine_utils