docs: Remove references to the long-defunct LLVM_USED_LIBS

LLVM_USED_LIBS hasn't done anything since 2012, stop telling people to
set it in the docs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@254173 91177308-0d34-0410-b5e6-96231b3b80d8

Author: bogner

docs/LibASTMatchersTutorial.rst

@@ -108,7 +108,6 @@ CMakeLists.txt should have the following contents:
 ::
 
       set(LLVM_LINK_COMPONENTS support)
-      set(LLVM_USED_LIBS clangTooling clangBasic clangAST)
 
       add_clang_executable(loop-convert
         LoopConvert.cpp

docs/RAVFrontendAction.rst

@@ -205,10 +205,10 @@ following CMakeLists.txt to link it:
 
 ::
 
-    set(LLVM_USED_LIBS clangTooling)
-
     add_clang_executable(find-class-decls FindClassDecls.cpp)
 
+    target_link_libraries(find-class-decls clangTooling)
+
 When running this tool over a small code snippet it will output all
 declarations of a class n::m::C it found: