Stop linking a copy of _json_c_strerror() (strerror_override.c) into the tests.

That hasn't been needed since since commit 6068d3f, which changed that code to
 check an env var instead ("_JSON_C_STRERROR_ENABLE").
Fixes issue #812, about dup symbols in static builds with clang.

tests/CMakeLists.txt

@@ -44,10 +44,6 @@ endif()
 foreach(TESTNAME ${ALL_TEST_NAMES})
 
 add_executable(${TESTNAME} ${TESTNAME}.c)
-if(${TESTNAME} STREQUAL test_strerror OR ${TESTNAME} STREQUAL test_util_file)
-# For output consistency, we need _json_c_strerror() in some tests:
-target_sources(${TESTNAME} PRIVATE ../strerror_override.c)
-endif()
 add_test(NAME ${TESTNAME} COMMAND ${PROJECT_SOURCE_DIR}/tests/${TESTNAME}.test)
 
 # XXX using the non-target_ versions of these doesn't work :(

tests/test_strerror.c

@@ -2,7 +2,6 @@
 #undef NDEBUG
 #endif
 #include "strerror_override.h"
-#include "strerror_override_private.h"
 
 #include <stdio.h>
 

tests/test_util_file.c

@@ -2,7 +2,6 @@
 #undef NDEBUG
 #endif
 #include "strerror_override.h"
-#include "strerror_override_private.h"
 #ifdef WIN32
 #define WIN32_LEAN_AND_MEAN
 #include <io.h>