don't print warning for prebuild step when finished

Author: leavez

lib/cocoapods-binary/Main.rb

@@ -97,6 +97,7 @@ def keep_source_code_for_prebuilt_frameworks!
     Pod::Podfile::DSL.enable_prebuild_patch false
     Pod::Config.force_disable_write_lockfile false
     Pod::Installer.disable_install_complete_message false
+    Pod::UserInterface.warnings = [] # clean the warning in the prebuild step, it's duplicated.
 
 
     # -- step 2: pod install ---