recipes: Delete superfluous assignments, S = ${WORKDIR}/${BP}

recipes: Delete superfluous assignments, S = ${WORKDIR}/${BP}

Given that bitbake.conf sets the default values:

BP = "${BPN}-${PV}"
S = "${WORKDIR}/${BP}"

there are a number of recipes that set the variable S completely
superfluously, so get rid of them.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>