[resultui] disable workbox sourcemap
[resultui] disable workbox sourcemap

So the Milo GAE tarball builds can be built reproducibly again.

R=nodir@google.com, 7f5d2f4f6ce87649784e35ad551490ab8d89e8eb@google.com

Change-Id: I3c0b3005dc1c4cd9940528ed2873d7f115835637
Bug: 1189309
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2771487
Reviewed-by: Quang Minh Tuan Nguyen <7f5d2f4f6ce87649784e35ad551490ab8d89e8eb@google.com>
Commit-Queue: Quang Minh Tuan Nguyen <7f5d2f4f6ce87649784e35ad551490ab8d89e8eb@google.com>
Auto-Submit: Weiwei Lin <968518a24f41fef00b747498600e52b792d06ae0@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go