[lldb] Remove unused POSIX ProcessMessage files

The last use of these was removed in cd44339.

Reviewed By: emaste

Differential Revision: https://reviews.llvm.org/D145559

Author: DavidSpickett

lldb/source/Plugins/Process/POSIX/CMakeLists.txt

@@ -1,7 +1,6 @@
 add_lldb_library(lldbPluginProcessPOSIX
   CrashReason.cpp
   NativeProcessELF.cpp
-  ProcessMessage.cpp
   ProcessPOSIXLog.cpp
 
   LINK_LIBS

lldb/source/Plugins/Process/POSIX/ProcessMessage.cpp

@@ -12,7 +12,6 @@ static_library("POSIX") {
   sources = [
     "CrashReason.cpp",
     "NativeProcessELF.cpp",
-    "ProcessMessage.cpp",
     "ProcessPOSIXLog.cpp",
   ]
 }