extend/ENV/super: set OPENSSL_NO_VENDOR

Many (~60) formulae in Homebrew/core set this manually to prevent the
`openssl` Rust crate from vendoring OpenSSL.

Let's make handling this simpler by setting it globally instead.

Library/Homebrew/extend/ENV/super.rb

@@ -86,6 +86,7 @@ module Superenv
     self["HOMEBREW_LIBRARY_PATHS"] = determine_library_paths
     self["HOMEBREW_DEPENDENCIES"] = determine_dependencies
     self["HOMEBREW_FORMULA_PREFIX"] = @formula.prefix unless @formula.nil?
+    self["OPENSSL_NO_VENDOR"] = "1"
 
     set_debug_symbols if debug_symbols