[lldb] Remove PluginInterface::GetPluginVersion

In all these years, we haven't found a use for this function (it has
zero callers). Lets just remove the boilerplate.

Differential Revision: https://reviews.llvm.org/D109600

lldb/source/Plugins/Process/scripted/ScriptedProcess.cpp

@@ -149,8 +149,6 @@ void ScriptedProcess::Terminate() {
 
 ConstString ScriptedProcess::GetPluginName() { return GetPluginNameStatic(); }
 
-uint32_t ScriptedProcess::GetPluginVersion() { return 1; }
-
 Status ScriptedProcess::DoLoadCore() {
   ProcessLaunchInfo launch_info = GetTarget().GetProcessLaunchInfo();