Revert "exec: load_script: don't blindly truncate shebang string"

Revert "exec: load_script: don't blindly truncate shebang string"

This reverts commit a1f041b053d219fceb1c04dcc844047b97f7c555.

It turns out that people do actually depend on the shebang string being
truncated, and on the fact that an interpreter (like perl) will often
just re-interpret it entirely to get the full argument list.

Reported-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>