Remove support for sksl_with_256_padding_seed_corpus.
Remove support for sksl_with_256_padding_seed_corpus.

The SkRuntimeEffect fuzzer no longer uses the final 256 bytes of each
shader as uniform data, making this corpus obsolete.

(Fuzzer corpus change: https://github.com/google/oss-fuzz/pull/7266 )

Change-Id: I3df9213520390249f401c83c13f0bca5c7f0dde4
Bug: skia:12781
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/508036
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Reviewed-by: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>
Commit-Queue: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia