keg: only prune var/homebrew/linked.
keg: only prune var/homebrew/linked.

`var/homebrew` is too broad and ends up deleting and recreating the
locks directory repeatedly.

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