cfl: switch to using the latest version of corpus

From the beginning CFL uses a corpus in Git submodule of a
lua-c-api-test repository, but this submodule was bumped quite
rarely and thus outdated corpus was used.
The patch switches to using the latest version of corpus.

Author: ligurio

.clusterfuzzlite/Dockerfile

@@ -12,6 +12,6 @@ RUN apt-get update && apt-get install -y \
 
 COPY . $SRC/lua-c-api-tests
 WORKDIR $SRC/lua-c-api-tests
-RUN git submodule update --init --recursive --force
-RUN cd corpus && git checkout cfl
+RUN rm -rf corpus
+RUN git clone --depth 1 --branch cfl https://github.com/ligurio/lua-c-api-corpus corpus
 COPY .clusterfuzzlite/build.sh $SRC/