It's been moved from /Applications/ to /System/Library/CoreServices/Applications/. Due to SIP, "Make Alias" is not available from the Finder's context menu in that directory, nor does the new Make Alias keyboard shortcut (Ctrl+Cmd+A - really, Apple?! Cmd+L does not appear to have even been reassigned!) work.
If you'd like a Finder alias for DVD Player in the Applications folder*, one can be created via AppleScript like so:
tell application "Finder" to make alias file to (POSIX file "/System/Library/CoreServices/Applications/DVD Player.app") at (POSIX file "/Applications")
* To its credit, Apple still provides the "CDs & DVDs" preference pane, which offers an option to open DVD Player when a video DVD is inserted, but some may prefer another action or to launch DVD Player manually to play VIDEO_TS files, etc.
/mac | Oct 23, 2018