remove explicit tools.apple_deployment_target_flag

two reasons for the change:

1. since Autotools adds apple deployement target flag conan#7862, AutoToolsBuildEnvironment calls tools.apple_deployment_target_flag on its own
2. Feature: add os.sdk sub-settings for Apple conan#8263 adds os.sdk sub-setting, Feature: add Apple Catalyst support (as new os.subsystem) conan#8264 adds os.subsystem sub-setting, they need to be passed to the tools.apple_deployment_target_flag

Specify library name and version: ICU/all

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.