fuzz-network-parser: drop ".network" and shorten names

All fuzzer inputs as .network files. Some had the suffix, others didn't.
So drop it everywhere, and also shorten some other names.

tools/check-directives.sh

@@ -34,8 +34,8 @@ function generate_directives() {
 ret=0
 if ! diff \
      <(generate_directives "$SOURCE_ROOT"/src/network/networkd-network-gperf.gperf | sort) \
-     <(sort "$SOURCE_ROOT"/test/fuzz/fuzz-network-parser/directives.network); then
-    echo "Looks like test/fuzz/fuzz-network-parser/directives.network hasn't been updated"
+     <(sort "$SOURCE_ROOT"/test/fuzz/fuzz-network-parser/directives); then
+    echo "Looks like test/fuzz/fuzz-network-parser/directives hasn't been updated"
     ret=1
 fi