blacklist: remove screen, libpcap, libiconv
blacklist: remove screen, libpcap, libiconv

Each has a formula in homebrew/dupes now

Closes Homebrew/homebrew#42212.

rwhogg/brew,MikeMcQuaid/brew,jmsundar/brew,pseudocody/brew,hanxue/linuxbrew,reelsense/brew,mahori/brew,JCount/brew,claui/brew,zmwangx/brew,gordonmcshane/homebrew,palxex/brew,gregory-nisbet/brew,reitermarkus/brew,ilovezfs/brew,amar-laksh/brew_sudo,ilovezfs/brew,bfontaine/brew,MikeMcQuaid/brew,rwhogg/brew,maxim-belkin/brew,vitorgalvao/brew,AnastasiaSulyagina/brew,nandub/brew,toonetown/homebrew,reitermarkus/brew,muellermartin/dist,reelsense/brew,aw1621107/brew,vitorgalvao/brew,nandub/brew,staticfloat/brew,palxex/brew,mahori/brew,mistydemeo/homebrew,Linuxbrew/brew,EricFromCanada/brew,toonetown/homebrew,MikeMcQuaid/brew,nandub/brew,bfontaine/brew,gregory-nisbet/brew,palxex/brew,mahori/brew,reitermarkus/brew,amar-laksh/brew_sudo,alyssais/brew,zmwangx/brew,sjackman/homebrew,JCount/brew,staticfloat/brew,EricFromCanada/brew,gordonmcshane/homebrew,zmwangx/brew,tonyg/homebrew,bfontaine/brew,DomT4/brew,EricFromCanada/brew,AnastasiaSulyagina/brew,mistydemeo/homebrew,mgrimes/brew,Linuxbrew/brew,hanxue/linuxbrew,mgrimes/brew,muellermartin/dist,vitorgalvao/brew,gordonmcshane/homebrew,gregory-nisbet/brew,claui/brew,Linuxbrew/brew,aw1621107/brew,MikeMcQuaid/brew,konqui/brew,mgrimes/brew,hanxue/linuxbrew,Linuxbrew/brew,reitermarkus/brew,ilovezfs/brew,vitorgalvao/brew,pseudocody/brew,jmsundar/brew,EricFromCanada/brew,tonyg/homebrew,sjackman/homebrew,pseudocody/brew,claui/brew,maxim-belkin/brew,tonyg/homebrew,alyssais/brew,konqui/brew,Homebrew/brew,toonetown/homebrew,claui/brew,jmsundar/brew,maxim-belkin/brew,staticfloat/brew,aw1621107/brew,mahori/brew,Homebrew/brew,Homebrew/brew,JCount/brew,konqui/brew,muellermartin/dist,alyssais/brew,reelsense/brew,rwhogg/brew,nandub/brew,DomT4/brew,konqui/brew,mistydemeo/homebrew,sjackman/homebrew,DomT4/brew,JCount/brew,amar-laksh/brew_sudo,DomT4/brew,sjackman/homebrew,Homebrew/brew,AnastasiaSulyagina/brew