Remove NPAPI command line flags entirely.

ContentShell now overrides IsNpapiEnabled() to enable NPAPI for testing.

BUG=493212
CQ_INCLUDE_TRYBOTS=tryserver.blink:win_blink_rel,mac_blink_rel

Review URL: https://codereview.chromium.org/1240543003

Cr-Commit-Position: refs/heads/master@{#339469}
9 files changed