stdenv: stop setting LD
stdenv: stop setting LD

superenv stopped setting LD in
8e4c0a141171666270529da4be026d529d474467, seems sensible to follow
suit in stdenv too.

See Homebrew/homebrew#14943.

Fixes Homebrew/homebrew#15090.
alyssais/brew,ilovezfs/brew,palxex/brew,Homebrew/brew,DomT4/brew,JCount/brew,reitermarkus/brew,EricFromCanada/brew,muellermartin/dist,rwhogg/brew,konqui/brew,zmwangx/brew,sjackman/homebrew,tonyg/homebrew,ilovezfs/brew,bfontaine/brew,sjackman/homebrew,JCount/brew,MikeMcQuaid/brew,JCount/brew,Linuxbrew/brew,toonetown/homebrew,EricFromCanada/brew,jmsundar/brew,palxex/brew,reelsense/brew,rwhogg/brew,toonetown/homebrew,aw1621107/brew,staticfloat/brew,maxim-belkin/brew,gregory-nisbet/brew,MikeMcQuaid/brew,konqui/brew,pseudocody/brew,claui/brew,vitorgalvao/brew,reelsense/brew,reelsense/brew,vitorgalvao/brew,mahori/brew,mistydemeo/homebrew,tonyg/homebrew,gordonmcshane/homebrew,mistydemeo/homebrew,alyssais/brew,tonyg/homebrew,pseudocody/brew,toonetown/homebrew,AnastasiaSulyagina/brew,AnastasiaSulyagina/brew,JCount/brew,alyssais/brew,gregory-nisbet/brew,mahori/brew,mahori/brew,konqui/brew,rwhogg/brew,hanxue/linuxbrew,amar-laksh/brew_sudo,DomT4/brew,mistydemeo/homebrew,AnastasiaSulyagina/brew,palxex/brew,mgrimes/brew,MikeMcQuaid/brew,claui/brew,bfontaine/brew,hanxue/linuxbrew,jmsundar/brew,zmwangx/brew,hanxue/linuxbrew,nandub/brew,jmsundar/brew,maxim-belkin/brew,reitermarkus/brew,EricFromCanada/brew,sjackman/homebrew,MikeMcQuaid/brew,DomT4/brew,mgrimes/brew,nandub/brew,muellermartin/dist,ilovezfs/brew,staticfloat/brew,EricFromCanada/brew,Homebrew/brew,aw1621107/brew,amar-laksh/brew_sudo,vitorgalvao/brew,mgrimes/brew,aw1621107/brew,nandub/brew,konqui/brew,staticfloat/brew,Homebrew/brew,pseudocody/brew,Linuxbrew/brew,nandub/brew,muellermartin/dist,Linuxbrew/brew,maxim-belkin/brew,gregory-nisbet/brew,vitorgalvao/brew,gordonmcshane/homebrew,claui/brew,reitermarkus/brew,DomT4/brew,mahori/brew,reitermarkus/brew,Homebrew/brew,claui/brew,Linuxbrew/brew,gordonmcshane/homebrew,bfontaine/brew,zmwangx/brew,amar-laksh/brew_sudo,sjackman/homebrew