v8: remove icu4c option (#16731)

Building against system-icu will be broken after the icu4c 59.1 upgrade
(#16720) and it's used in <1% of all v8 installs.

Formula/v8.rb

@@ -22,7 +22,6 @@ class V8 < Formula
 
   depends_on :python => :build # gyp doesn't run under 2.6 or lower
   depends_on "readline" => :optional
-  depends_on "icu4c" => :optional
 
   needs :cxx11
 
@@ -75,13 +74,6 @@ class V8 < Formula
     # https://code.google.com/p/v8/issues/detail?id=4511#c3
     ENV.append "GYP_DEFINES", "v8_use_external_startup_data=0"
 
-    if build.with? "icu4c"
-      ENV.append "GYP_DEFINES", "use_system_icu=1"
-      i18nsupport = "i18nsupport=on"
-    else
-      i18nsupport = "i18nsupport=off"
-    end
-
     # fix up libv8.dylib install_name
     # https://github.com/Homebrew/homebrew/issues/36571
     # https://code.google.com/p/v8/issues/detail?id=3871
@@ -99,7 +91,7 @@ class V8 < Formula
     (buildpath/"tools/clang").install resource("clang")
 
     system "make", "native", "library=shared", "snapshot=on",
-                   "console=readline", i18nsupport,
+                   "console=readline", "i18nsupport=off",
                    "strictaliasing=off"
 
     include.install Dir["include/*"]