[Target] Remove Process::GetObjCLanguageRuntime

Summary:
In an effort to make Process more language agnostic, I removed
GetCPPLanguageRuntime from Process. I'm following up now with an equivalent
change for ObjC.

Differential Revision: https://reviews.llvm.org/D63052

llvm-svn: 362981
diff --git a/lldb/source/Plugins/Language/ObjC/NSString.cpp b/lldb/source/Plugins/Language/ObjC/NSString.cpp
index 1d77f8f..4800c95 100644
--- a/lldb/source/Plugins/Language/ObjC/NSString.cpp
+++ b/lldb/source/Plugins/Language/ObjC/NSString.cpp
@@ -59,7 +59,7 @@
   if (!process_sp)
     return false;
 
-  ObjCLanguageRuntime *runtime = process_sp->GetObjCLanguageRuntime();
+  ObjCLanguageRuntime *runtime = ObjCLanguageRuntime::Get(*process_sp);
 
   if (!runtime)
     return false;