Remove call to pod clean from ios_build_preflight

This call could lead to long wait times, in particular in WordPress iOS,
as every pod was downloaded from scratch.

See:

- woocommerce/woocommerce-ios#7649
- wordpress-mobile/WordPress-iOS#19033 (comment)

Author: mokagio

lib/fastlane/plugin/wpmreleasetoolkit/actions/ios/ios_build_preflight.rb

@@ -33,7 +33,6 @@ def self.run(params)
           raise
         end
 
-        Action.sh('rake dependencies:pod:clean')
         other_action.cocoapods()
       end