sphinx-doc: remove postinstall
sphinx-doc: remove postinstall

LinuxbrewTestBot/homebrew-core,LinuxbrewTestBot/homebrew-core,Linuxbrew/homebrew-core,rwhogg/homebrew-core,maxim-belkin/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core,maxim-belkin/homebrew-core