Revert "wg-quick: wait on process substitutions"

Revert "wg-quick: wait on process substitutions"

This reverts commit 26683f6c9ad18d9914b23312c221f27fd5ecab51, which
means the old problem comes back. That's an issue. But waiting on
process substitutions is not available with commonly used bash versions:

  # wg-quick up demo
  [#] ip link add demo type wireguard
  [#] wg setconf demo /dev/fd/63
  /usr/bin/wg-quick: line 251: wait: pid 2955 is not a child of this shell
  [#] ip link delete dev demo

This means we have to wait a few years before fixing this issue. IOW,
bash limitation; can't fix.

Reported-by: Theodore Mozzo <theodore.mozzo@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>