autoroll: Update Clang script path.
autoroll: Update Clang script path.

tools/clang/scripts/update.sh was deleted in
https://chromium.googlesource.com/chromium/src/+/656a6433abb41ba076c337b9ffb8c8899c3f20b7
so now the update.py is used on all platforms.
Update our autoroll script accordingly.

NOTRY=True

Review URL: https://codereview.webrtc.org/1493683003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#10879}

ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc