don't copy core kmod source files to tempdir

No need to copy them anymore now that the core kmod is getting
built elsewhere.
Merge pull request #20 from jpoimboe/copy-core-fix

don't copy core kmod source files to tempdir
fix STRIPCMD use

bash gets confused when a command and its args are quoted:

  /usr/local/libexec/kpatch/kpatch-build: line 131: strip -d --keep-file-symbols: command not found
Merge pull request #21 from jpoimboe/strip-fix

fix STRIPCMD use