klibc.inc: remove ${PR} leftover

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
klibc: ensure package strip logic stays the same after oe-core package.bbclass changes

See http://patches.openembedded.org/patch/65311/

Signed-off-by: Koen Kooi <koen.kooi@linaro.org>