Remove support for Intel classic compiler

Remove support for Intel classic compiler

This compiler has sometimes generated the fastest code, but also most
often generated the wrong code of any supported compiler. Since Intel
now has another clang-based compiler that they are targetting for GPU
support in oneAPI, we've chosen to support it. Our resources are
limited so something else has to go.

Minor improvements to the install guide while I was there.

Added a fatal error to CMake as otherwise we will get bug reports that
icc doesn't work.

Added release notes

Fixes #3893