Drop download feature

[termoshtt]

Ready for #76. This also disable Windows and macOS CI because they needs download feature.

[termoshtt]

There are two problems while intel-mkl-sys tests:

Does not link to MKL for mkl-static-*-* case

   = note: /usr/bin/ld: /__w/intel-mkl-src/intel-mkl-src/target/debug/deps/intel_mkl_sys-d187510431f14014.fffzkjh3qo1ov3i.rcgu.o: in function `intel_mkl_sys::tests::cos':
          /__w/intel-mkl-src/intel-mkl-src/intel-mkl-sys/src/lib.rs:48: undefined reference to `vdCos'
          /usr/bin/ld: /__w/intel-mkl-src/intel-mkl-src/target/debug/deps/intel_mkl_sys-d187510431f14014.fffzkjh3qo1ov3i.rcgu.o: in function `intel_mkl_sys::tests::new_stream':
          /__w/intel-mkl-src/intel-mkl-src/intel-mkl-sys/src/lib.rs:59: undefined reference to `vslNewStream'
          collect2: error: ld returned 1 exit status

libiomp5.so cannot load for mkl-dynamic-*-iomp

/__w/intel-mkl-src/intel-mkl-src/target/debug/deps/intel_mkl_sys-4814989dfea38350: error while loading shared libraries: libiomp5.so: cannot open shared object file: No such file or directory
error: test failed, to rerun pass '--lib'
Error: The process '/usr/local/cargo/bin/cargo' failed with exit code 127

These problems will be fixed in #81