useradd.bbclass: Remove base-passwd dependency

useradd.bbclass: Remove base-passwd dependency

shadow-sysroot (another useradd dependency) recipe already includes
base-passwd dependency, so removing it from useradd class.

This fixes the compilation issue observed when a recipe depends
on another where the latter inherits from useradd as in the
following scenario:

https://bugzilla.yoctoproject.org/show_bug.cgi?id=7724#c0

[Yocto #7724]

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>