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