Remove unnecessary fuzztest:: in fuzz_dec_incr (#3036)

tests/gtest/avif_fuzztest_dec_incr.cc

diff --git a/tests/gtest/avif_fuzztest_dec_incr.cc b/tests/gtest/avif_fuzztest_dec_incr.cc
index 2bdb7d1..fc3bc2f 100644
--- a/tests/gtest/avif_fuzztest_dec_incr.cc
+++ b/tests/gtest/avif_fuzztest_dec_incr.cc
@@ -115,7 +115,7 @@
     .WithDomains(ArbitraryImageWithSeeds({AVIF_APP_FILE_FORMAT_AVIF}),
                  /*is_persistent=*/Arbitrary<bool>(),
                  /*give_size_hint=*/Arbitrary<bool>(),
-                 fuzztest::BitFlagCombinationOf<avifImageContentTypeFlags>(
+                 BitFlagCombinationOf<avifImageContentTypeFlags>(
                      {AVIF_IMAGE_CONTENT_COLOR_AND_ALPHA,
                       AVIF_IMAGE_CONTENT_GAIN_MAP,
                       AVIF_IMAGE_CONTENT_SAMPLE_TRANSFORMS}),