"Cancelled" to "Canceled" in en-US strings.
"Canceled" appears to be the favored spelling in en-US. Both forms are
used in similar frequencies in the codebase (~2500 vs. ~2200 lines).
This change updates user visible strings to use 'Canceled' for
consistency.
Relevant NGram: https://books.google.com/ngrams/graph?content=canceled%2Ccancelled&case_insensitive=on&year_start=1800&year_end=2014&corpus=5&smoothing=3
BUG=262545
Review URL: https://codereview.chromium.org/
827123002
Cr-Commit-Position: refs/heads/master@{#309777}