[GN] Remove CAN_USE_VFP_INSTRUCTIONS define to match GYP

CAN_USE_VFP_INSTRUCTIONS was removed in GYP in
https://codereview.chromium.org/340373002

BUG=None
LOG=Y

Review URL: https://codereview.chromium.org/1635123003

Cr-Commit-Position: refs/heads/master@{#33526}

BUILD.gn

@@ -1740,8 +1740,6 @@ source_set("v8_libbase") {
 
     libs = [ "dl", "rt" ]
   } else if (is_android) {
-    defines += [ "CAN_USE_VFP_INSTRUCTIONS" ]
-
     if (current_toolchain == host_toolchain) {
       libs = [ "dl", "rt" ]
       if (host_os == "mac") {