wasm-reduce: Do not verify binary roundtripping when not using binary files

[kripken]

A reduction on text files may be done on text because binary writing is
where the bug is.

Diff is 99% whitespace.

[aheejin]

Don't try roundtripping to binary sounds right to me when not using binary, but I'm not sure what "binary writing is where the bug is" means..?

[kripken]

Sorry, by "binary writing is where the bug is" I meant that I had a bug in binary writing. I ran the reducer on text to get a testcase for it, so the testcase was "write the binary and check for a crash". That's when I noticed the issue here.

[kripken]

Actually I changed my mind here. I think it is good to verify that reading and writing the input works even when not reducing on binary. But the comments were confusing, which is why I was mixed up before. I fixed those now.