Move aom_obu_type_to_string from exports_test to exports_dec

This is where it's really needed: obu_parser.cc needs it.

Change-Id: I8ebe48807a6d828b78b5cfcd38a5c6f4d94c94e2
diff --git a/aom/exports_dec b/aom/exports_dec
index 6c1d754..d7d1c4f 100644
--- a/aom/exports_dec
+++ b/aom/exports_dec
@@ -6,4 +6,5 @@
 text aom_codec_register_put_frame_cb
 text aom_codec_register_put_slice_cb
 text aom_codec_set_frame_buffer_functions
+text aom_obu_type_to_string
 text aom_read_obu_header
diff --git a/aom/exports_test b/aom/exports_test
index 5e0ac78..eff93db 100644
--- a/aom/exports_test
+++ b/aom/exports_test
@@ -9,7 +9,6 @@
 text aom_noise_model_get_grain_parameters
 text aom_noise_model_save_latest
 text aom_noise_model_update
-text aom_obu_type_to_string
 text aom_scale_rtcd
 text aom_wb_write_literal
 text aom_wb_write_unsigned_literal