openpower-pels: clean up various compile warnings

Compile warnings observed when compiling parts of the
openpower-pels (or corresponding tests) under stricter
compiler warning flags of Meson.

Issues fixed:
    - many unused parameters
    - invalid case fall-through
    - excess semi-colons
    - incorrect 'const' on return-by-value type
    - removal of variable length array in test case
    - uncaught return from 'system' call in test case

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I8af69184042cf8661d1307a02ecf3afcab4724a1
diff --git a/extensions/openpower-pels/extended_user_data.cpp b/extensions/openpower-pels/extended_user_data.cpp
index 0731b60..6370459 100644
--- a/extensions/openpower-pels/extended_user_data.cpp
+++ b/extensions/openpower-pels/extended_user_data.cpp
@@ -100,8 +100,9 @@
 }
 
 std::optional<std::string>
-    ExtendedUserData::getJSON(uint8_t creatorID,
-                              const std::vector<std::string>& plugins) const
+    ExtendedUserData::getJSON(uint8_t /*creatorID*/,
+                              const std::vector<std::string>& plugins
+                              [[maybe_unused]]) const
 {
     // Use the creator ID value from the section.
 #ifdef PELTOOL