Remove CORE_UTIL_EXPORT

[ Merge of http://go/wvgerrit/155070 ]

These functions are internal utilities and should not be exported from
our library.  IIRC, this was added to aid in Windows tests, but this is
no longer needed.

Bug: 236317198
Test: build_and_run_all_unit_tests.sh
Change-Id: I19beb35a15f0f87dc8f968e1dd5302aed9463e54

libwvdrmengine/Android.bp

@@ -338,7 +338,6 @@ cc_library_static {
     ],
 
     cflags: [
-        "-DCORE_UTIL_IMPLEMENTATION",
         "-DIS_HIDL",
     ],
 
@@ -371,8 +370,6 @@ cc_library_static {
         "liblog",
     ],
 
-    cflags: ["-DCORE_UTIL_IMPLEMENTATION"],
-
     srcs: cdm_util_src_files,
 
 }