oss-fuzz.sh: just install the shared library

The workaround is no longer necessary, because the scripts
checking fuzzers have stopped going down to the subdirectories
of $OUT and started to look for the string "LLVMFuzzerTestOneInput"
to tell fuzzers and random binaries apart. Some more details can be
found at https://github.com/google/oss-fuzz/issues/1566.