Installed Cuda toolkit 7.5, but libcudart.so.5.5 remains

Question

After installing Cuda Toolkit 7.5 on Ubuntu 14.04 (via apt-get of .deb file, followed by update of nvidia driver to 352.63), nvcc --version, NVidia-smi, and cuda samples work as expected.

7.5 is installed in /usr/local/cuda-7.5, with /usr/local/cuda soft-linked to that location.

The file /etc/profile.d/cuda-7-5.sh contains just the line:

PATH=/usr/local/cuda/bin:$PATH

And both /etc/ld.so.conf.d/cuda-7-5.conf and /etc/ld.so.conf.d/cuda-7-5.sh contain just the line:

/usr/local/cuda/lib64

However, the system still contains /usr/lib/x86_64-linux-gnu/libcudart.so.5.5.

Questions:

1. Why is /usr/lib/x86_64-linux-gnu/libcudart.so.5.5 still present? Is it required, or can it be removed? What are the steps for removing it, and will 7.5 need to be reinstalled?

2. Are the contents of /etc/ld.so.conf.d/cuda-7-5.sh correct, or should it be as follows?:

   LD_LIBRARY_PATH=/usr/local/cuda/lib64:$LD_LIBRARY_PATH