[server/tsmon] rename c to ctx
[server/tsmon] rename c to ctx

and rename TsMon to TSMon to make tricium happier

Bug: 1006921
Change-Id: If992c16ea3f0413ec6cf88005a307e27e4ab523a
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3388600
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Commit-Queue: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>

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