suricata: clean some disk space while building (#11797)

As done by openssl in #11618

Is there a way from build.sh to know if we are built by CIFuzz ? Like
environment variable `CFL_PLATFORM` ?
Because I do not think we want to build other branches than master for
CIFuzz

Author: catenacyber

projects/suricata/build.sh

@@ -131,6 +131,11 @@ cat generic.dict >> $OUT/fuzz_applayerparserparse$branch.dict
 cat generic.dict >> $OUT/fuzz_sigpcap$branch.dict
 cat generic.dict >> $OUT/fuzz_sigpcap_aware$branch.dict
 
+df
+# clean to leave enough space for CIFuzz
+make clean
+df
+
 # build corpuses
 # default configuration file
 zip -r $OUT/fuzz_confyamlloadstring"$branch"_seed_corpus.zip suricata.yaml