Rename tools-webrtc -> tools_webrtc

This aligns with established naming convention for all
other directories.

BUG=webrtc:7593
NOTRY=True
NOTREECHECKS=True
R=ehmaldonado@webrtc.org, mbonadei@webrtc.org
TBR=henrika@webrtc.org

Review-Url: https://codereview.webrtc.org/2864213004 .
Cr-Commit-Position: refs/heads/master@{#18059}

DEPS

diff --git a/DEPS b/DEPS
index c0eb634..5be4d77 100644
--- a/DEPS
+++ b/DEPS
@@ -165,7 +165,7 @@
         'python',
         'src/build/landmines.py',
         '--landmine-scripts',
-        'src/tools-webrtc/get_landmines.py',
+        'src/tools_webrtc/get_landmines.py',
         '--src-dir',
         'src',
     ],