Renaming system.gyp:ssl to system.gyp:nss and removing unused BUILD.gn

BUG=604728
TBR=thakis@chromium.org, jbauman@chromium.org

Review-Url: https://codereview.chromium.org/1918303002
Cr-Commit-Position: refs/heads/master@{#390962}
12 files changed