pldmd: Remove unused MCTP_MSG_TYPE_PLDM

```
../pldmd/pldmd.cpp:67:19: error: unused variable 'MCTP_MSG_TYPE_PLDM' [-Werror,-Wunused-const-variable]
   67 | constexpr uint8_t MCTP_MSG_TYPE_PLDM = 1;
      |                   ^~~~~~~~~~~~~~~~~~
```

Change-Id: I12724e6639ad359b9b8cba4cf523ce86b8bd6d24
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/pldmd/pldmd.cpp b/pldmd/pldmd.cpp
index 8695fe8..39e1213 100644
--- a/pldmd/pldmd.cpp
+++ b/pldmd/pldmd.cpp
@@ -64,7 +64,6 @@
 #include "oem_ibm.hpp"
 #endif
 
-constexpr uint8_t MCTP_MSG_TYPE_PLDM = 1;
 constexpr const char* PLDMService = "xyz.openbmc_project.PLDM";
 
 using namespace pldm;