Remove boost::to_lower_copy

Replaced with inline std::transform lambda for lowercase conversion,
removing Boost dependency.

Tested: added UT and verified all tests passed

Change-Id: Ie875e131b2e0a7d5ab53288928983d640a9d1c12
Signed-off-by: George Liu <liuxiwei@ieisystem.com>
diff --git a/src/entity_manager/utils.cpp b/src/entity_manager/utils.cpp
index 4e46395..86024c5 100644
--- a/src/entity_manager/utils.cpp
+++ b/src/entity_manager/utils.cpp
@@ -5,7 +5,6 @@
 #include "expression.hpp"
 #include "phosphor-logging/lg2.hpp"
 
-#include <boost/algorithm/string/case_conv.hpp>
 #include <phosphor-logging/lg2.hpp>
 #include <sdbusplus/bus/match.hpp>
 
@@ -291,8 +290,7 @@
                                      const std::string& boardType)
 {
     std::string path = "/xyz/openbmc_project/inventory/system/";
-    std::string boardTypeLower = boost::algorithm::to_lower_copy(boardType);
-
+    std::string boardTypeLower = toLowerCopy(boardType);
     std::regex_replace(boardName.begin(), boardName.begin(), boardName.end(),
                        illegalDbusMemberRegex, "_");