debug: dlv-dap installation instruction in the popup is incorrect

[hyangah]

For dlv-dap, we need to rename it to dlv-dap.
Or maybe we can just omit this and give a link to the manual instruction documentation.

cc @suzmue

[gopherbot]

Change https://golang.org/cl/307054 mentions this issue: src/goInstallTools.ts: update install instructions for dlv-dap