git: Remove .gitattributes

This change allow building UnifySDK on github.

Removing LFS objects is a good start to slim down UnifySDK repo

Observed issue:

    (...)
    #11 538.0 100% tests passed, 0 tests failed out of 69
    #11 538.0 Total Test time (real) = 287.70 sec
    #11 538.0 cmake --build build --target package
    (...)
    #11 538.2 [2/3] Run CPack packaging tool...
    #11 538.2 CPack: Create package using DEB
    #11 538.2 CPack: Install projects
    #11 538.2 CPack: - Install project: uic []
    #11 538.2 CPack: -   Install component: libunify-dev
    #11 538.7 CMake Error at /usr/local/opt/unifysdk/build/components/cmake_install.cmake:195 (file):
    #11 538.7   file INSTALL cannot copy file

Relate-to: SiliconLabsSoftware/z-wave-engine-application-layer#11
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr