external-sourcery-toolchain: kill ${exec_prefix}/lib/locale in do_install_locale

As do_install_locale already copied these into the sysroot to be picked up by
eglibc-locale, there's no reason to keep the files around for ourselves.

Note: this should go into the oe-core eglibc-package.inc.

Signed-off-by: Christopher Larson <chris_larson@mentor.com>