Privatize useful.h and avl.h
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index 90ba2a7..c929475 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -850,7 +850,6 @@
include/grpc/support/atm_gcc_atomic.h \
include/grpc/support/atm_gcc_sync.h \
include/grpc/support/atm_windows.h \
-include/grpc/support/avl.h \
include/grpc/support/cmdline.h \
include/grpc/support/cpu.h \
include/grpc/support/host_port.h \
@@ -870,7 +869,6 @@
include/grpc/support/tls_gcc.h \
include/grpc/support/tls_msvc.h \
include/grpc/support/tls_pthread.h \
-include/grpc/support/useful.h \
include/grpc/support/workaround_list.h \
src/core/README.md \
src/core/ext/README.md \
@@ -1074,6 +1072,7 @@
src/core/lib/gpr/arena.h \
src/core/lib/gpr/atm.cc \
src/core/lib/gpr/avl.cc \
+src/core/lib/gpr/avl.h \
src/core/lib/gpr/cmdline.cc \
src/core/lib/gpr/cpu_iphone.cc \
src/core/lib/gpr/cpu_linux.cc \
@@ -1121,6 +1120,7 @@
src/core/lib/gpr/tmpfile_msys.cc \
src/core/lib/gpr/tmpfile_posix.cc \
src/core/lib/gpr/tmpfile_windows.cc \
+src/core/lib/gpr/useful.h \
src/core/lib/gpr/wrap_memcpy.cc \
src/core/lib/gprpp/README.md \
src/core/lib/gprpp/abstract.h \