[ios][PhishGuard] Remove PASSWORD_REUSE_DETECTION_ENABLED compile flag

Design doc: go/bling-phishguard

The PASSWORD_REUSE_DETECTION_ENABLED flag disabled compiling of code
in iOS. Previous CLs either 1) removed the compile flag from disabling
whole classes or methods, or 2) replaced the compile flag with a
runtime flag that is disabled on iOS.

This CL will land after all uses of PASSWORD_REUSE_DETECTION_ENABLED
have been removed.

Bug: 1147962
Change-Id: Ia82ea36bb75cb431dc0b9f42cdc7b7b7118b5373
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536842
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828476}

components/password_manager/core/browser/BUILD.gn

@@ -11,15 +11,11 @@ if (is_android) {
 
 # TODO(crbug.com/1006430): Fix password reuse detection not fully functional on
 # Android.
-password_reuse_detection_support = !is_ios
 password_reuse_warning_support = !is_ios
 password_on_focus_ping_support = !is_ios
 
 config("password_reuse_detection_config") {
   defines = []
-  if (password_reuse_detection_support) {
-    defines += [ "PASSWORD_REUSE_DETECTION_ENABLED" ]
-  }
   if (password_reuse_warning_support) {
     defines += [ "PASSWORD_REUSE_WARNING_ENABLED" ]
   }