lkft-metadata.bbclass: write SRC_URI first line to srcuri0
lkft-metadata.bbclass: write SRC_URI first line to srcuri0

* get rid of srcurifile variable, it's used only once.
* filter out empty lines from srcuri because there's cases where we can
  end with a blank line at the beginning. e.g. SRC_URI = " \
* write srcuri0 in a format that we can use directly.
* don't bother writing if SRC_URI isn't found.

Signed-off-by: Fathi Boudra <7cd6e55cc07a66bc71d7901a4cddfe6c22aab659@linaro.org>

96boards/meta-rpb,fboudra/meta-rpb,fboudra/meta-rpb,fboudra/meta-rpb,96boards/meta-rpb