libav: actively prevent X11 linkage
libav: actively prevent X11 linkage

Properly fixes #64654. Also fixes license.

Note the following:
* New patch was cherry-picked from upstream commit that is in HEAD, but not included in the current release, even though the fix predates it. Cherry-picking was necessary because the second hunk in the commit fails to apply against current release.
* When checking with upstream how the above happened, I received unofficial confirmation that this project is no longer maintained:
  * Email:
    * Last meaningful comms on dev mailing list almost a year ago
    * Query on project status in April 2020 netted one reply from a libav contributor: "It's dead" (https://lists.libav.org/pipermail/libav-devel/2020-April/thread.html)
    * My own query on official status has not yet been responded to
  * IRC:
    * My queries on #libav-devel net only off-the-record responses that no one is working on libav, but no one's willing to "call time of death", so there will probably not be an official announcement on libav.org

Since Homebrew libav installs still number in the thousands, I'm fixing the opportunistic X11 linkage, but recommend deprecation as of last GitHub commit (16 Apr 2019)

Closes #65345.

Signed-off-by: FX Coudert <c329953660db96eae534be5bbf1a735c2baf69b5@gmail.com>
Signed-off-by: BrewTestBot <8a898ee6867e4f2028e63d2a6319b2224641c06c@users.noreply.github.com>

mbcoguno/homebrew-core,mbcoguno/homebrew-core,nbari/homebrew-core,mfikes/homebrew-core,mbcoguno/homebrew-core,makigumo/homebrew-core,adam-moss/homebrew-core,spaam/homebrew-core,chrisfinazzo/homebrew-core,makigumo/homebrew-core,lemzwerg/homebrew-core,zyedidia/homebrew-core,chrisfinazzo/homebrew-core,adam-moss/homebrew-core,nbari/homebrew-core,filcab/homebrew-core,stgraber/homebrew-core,zyedidia/homebrew-core,spaam/homebrew-core,cblecker/homebrew-core,Moisan/homebrew-core,Linuxbrew/homebrew-core,dsXLII/homebrew-core,uyjulian/homebrew-core,Moisan/homebrew-core,nandub/homebrew-core,Homebrew/homebrew-core,cblecker/homebrew-core,lemzwerg/homebrew-core,Linuxbrew/homebrew-core,Homebrew/homebrew-core,JCount/homebrew-core,filcab/homebrew-core,stgraber/homebrew-core,sjackman/homebrew-core,JCount/homebrew-core,sjackman/homebrew-core,mfikes/homebrew-core,uyjulian/homebrew-core,nandub/homebrew-core,dsXLII/homebrew-core