[build] Remove support for building with the Intel C compiler

[build] Remove support for building with the Intel C compiler

Support for building with the Intel C compiler (icc) was added in 2009
in the expectation that UEFI support would eventually involve
compiling iPXE to EFI Byte Code.

EFI Byte Code has never found any widespread use: no widely available
compilers can emit it, Microsoft refuses to sign EFI Byte Code
binaries for UEFI Secure Boot, and I have personally never encountered
any examples of EFI Byte Code in the wild.

The support for using the Intel C compiler has not been tested in over
a decade, and would almost certainly require modification to work with
current releases of the compiler.

Simplify the build process by removing this old legacy code.

Signed-off-by: Michael Brown <mcb30@ipxe.org>