perf: remove x-axis ticks and replace with a single label
perf: remove x-axis ticks and replace with a single label

Change-Id: I443cbad5273c7f9febf9be2e4acdb25b1bbb0412
Reviewed-on: https://go-review.googlesource.com/c/build/+/412376
Reviewed-by: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>

golang/build,golang/build,golang/build,golang/build