[lldb] Return StringRef from PluginInterface::GetPluginName

There is no reason why this function should be returning a ConstString.

While modifying these files, I also fixed several instances where
GetPluginName and GetPluginNameStatic were returning different strings.

I am not changing the return type of GetPluginNameStatic in this patch, as that
would necessitate additional changes, and this patch is big enough as it is.

Differential Revision: https://reviews.llvm.org/D111877

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

@@ -145,8 +145,6 @@ void ScriptedProcess::Terminate() {
   PluginManager::UnregisterPlugin(ScriptedProcess::CreateInstance);
 }
 
-ConstString ScriptedProcess::GetPluginName() { return GetPluginNameStatic(); }
-
 Status ScriptedProcess::DoLoadCore() {
   ProcessLaunchInfo launch_info = GetTarget().GetProcessLaunchInfo();