Don't explicitly set clone child ptrace options

Don't explicitly set clone child ptrace options

linux_handle_extended_wait calls target_post_attach if we're handling
a PTRACE_EVENT_CLONE, and libthread_db.so isn't active.
target_post_attach just calls linux_init_ptrace_procfs to set the
lwp's ptrace options.  However, this is completely unnecessary,
because, as man ptrace [1] says, options are inherited:

  "Flags are inherited by new tracees created and "auto-attached" via
   active PTRACE_O_TRACEFORK, PTRACE_O_TRACEVFORK, or PTRACE_O_TRACECLONE
   options."

This removes the unnecessary call.

[1] - https://man7.org/linux/man-pages/man2/ptrace.2.html

Approved-By: Simon Marchi <simon.marchi@efficios.com>
Change-Id: I533eaa60b700f7e40760311fc0d344d0b3f19a78