Revert "llvm: fix LLVMWindowsManifest not finding libxml2"

This reverts commit 4ff3e836.

It wasn't the right fix for linking errors. Furthermore, the patched
code should not get executed as libxml2 is now disabled in llvm.

projects/unix/llvm.cmake

@@ -24,7 +24,5 @@ superbuild_add_project(llvm
 
 superbuild_apply_patch(${project} workaround-intel-build-failures
   "Fix build failures with the Intel compiler")
-superbuild_apply_patch(${project} fix-libxml2
-  "Fix -lxml2-not-found problem")
 
 set(llvm_dir "<INSTALL_DIR>")

projects/unix/patches/llvm-fix-libxml2.patch

---- src/cmake/config-ix.cmake	2018-11-07 19:10:31.910221296 +0000
-+++ src/cmake/config-ix.cmake	2018-11-07 19:02:58.794960316 +0000
-@@ -153,7 +153,7 @@
-         else()
-           include_directories(${LIBXML2_INCLUDE_DIR})
-         endif()
--        set(LIBXML2_LIBS "xml2")
-+        set(LIBXML2_LIBS ${LIBXML2_LIBRARY})
-       endif()
-     endif()
-   endif()