libs.mk, testdata: rm redundant test of LIBVPX_TEST_DATA

the return value of enabled, which may be empty, is handled by the for
loop. this avoids making an unnecessarily long command line which may
fail in certain cases.

Change-Id: Ib88ecbbe2c0f6d7debb600b4caed4884497263b1

libs.mk

@@ -429,12 +429,10 @@ testdata:: $(LIBVPX_TEST_DATA)
           if [ -n "$${sha1sum}" ]; then\
             set -e;\
             echo "Checking test data:";\
-            if [ -n "$(LIBVPX_TEST_DATA)" ]; then\
-                for f in $(call enabled,LIBVPX_TEST_DATA); do\
-                    grep $$f $(SRC_PATH_BARE)/test/test-data.sha1 |\
-                        (cd $(LIBVPX_TEST_DATA_PATH); $${sha1sum} -c);\
-                done; \
-            fi; \
+            for f in $(call enabled,LIBVPX_TEST_DATA); do\
+                grep $$f $(SRC_PATH_BARE)/test/test-data.sha1 |\
+                    (cd $(LIBVPX_TEST_DATA_PATH); $${sha1sum} -c);\
+            done; \
         else\
             echo "Skipping test data integrity check, sha1sum not found.";\
         fi