the libc takes care of trying execve as many times as needed for
execvp, it's not a kernel call.
Also, sneak a double-free fix (desc was not reset properly in case
load_elf_desc_shebang failed)
Fixes: b1681f4a3affff ("mcexec/execve: fix shebangs handling")
Change-Id: If8e3d7ae53acdeffc0331ae8621e0832fcfa406f