[caffe2] Remove cxx override to c++17 (#108687)
Summary: Allow the user to specify the cxx version to use when compiling. For applications that compile with C++20, we wish to also compile this library with C++20 to avoid subtle ODR violations with using different library standards.
Test Plan: Built the project successfully.
Reviewed By: smeenai
Differential Revision: D48636406
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108687
Approved by: https://github.com/davidberard98
