In 9d1344ba (fuzz: Automatically export all tests pickles into
fuzz/corpus) I added code that automatically exports all test pickles
to fuzz corpus, so that fuzzing starts from all the tricky cases we
already put into tests. However exported files were named as
test-i-j.pickle, where i is sequential number of test entry in global
test vector. This way if we insert some new entry in the middle, or
change entries order it causes lots of renaming inside fuzz/corpus/ on
next `go generate`.

-> Fix that by emitting vectors as test-<sha1-of-pickle>.pickle so that
file name depends only on pickle content are remains stable
independently of entry position in the list of tests.

Besides changes to fuzz_test.go this patch brings:

1) rm fuzz/corpus/test-*.pickle
2) `go generate`

The result inside fuzz/corpus/ is pure renaming + removal of duplicates.
For example test-15-4.pickle is removed because the same data was in test-14-4.pickle
and now resides in test-ee4459c0c165c4cbc3672ee5ef5438e00121b229.pickle.