PEL: switch fmt::format to use std::format

fmt::format is supported in the c++ std. This will
    help to remove fmt package dependency.

Change-Id: I89f0a5b67bbfe54168a20e93c989a1ae87f54503
Signed-off-by: Jayanth Othayoth <ojayanth@in.ibm.com>
diff --git a/extensions/openpower-pels/user_data.cpp b/extensions/openpower-pels/user_data.cpp
index 0b07b8b..a24a8f3 100644
--- a/extensions/openpower-pels/user_data.cpp
+++ b/extensions/openpower-pels/user_data.cpp
@@ -22,10 +22,10 @@
 #include "user_data_json.hpp"
 #endif
 
-#include <fmt/format.h>
-
 #include <phosphor-logging/log.hpp>
 
+#include <format>
+
 namespace openpower
 {
 namespace pels
@@ -64,7 +64,7 @@
     catch (const std::exception& e)
     {
         log<level::ERR>(
-            fmt::format("Cannot unflatten user data: {}", e.what()).c_str());
+            std::format("Cannot unflatten user data: {}", e.what()).c_str());
         _valid = false;
     }
 }
@@ -88,7 +88,7 @@
     if (header().id != static_cast<uint16_t>(SectionID::userData))
     {
         log<level::ERR>(
-            fmt::format("Invalid UserData section ID: {0:#x}", header().id)
+            std::format("Invalid UserData section ID: {0:#x}", header().id)
                 .c_str());
         _valid = false;
     }