Fix unix test build by removing unnecessary 'managed_test_build' semafore file

Fix unix test build by removing unnecessary 'managed_test_build' semafore file

Fixes #17503

The error is caused by both:

1. Unnecessary usage of 'managed_test_build' semaphore file which is incorrectly
   set after /t:BatchRestorePackages build target and prevents managed test build
   which is invoked after semaphore alredy exists
2. Masked by the above error is a wrong condition in dirs.proj non-windows test build
   which was introduced by PR #17161 and which prevented unix build due to missing
   #17161 group build port to unix