IO flushed twice if using JSON.build or YAML.build

[matthewmcgarvey]

JSON

1. crystal/src/json/builder.cr

   Line 56 in 3b5bc55

   @io.flush

2. crystal/src/json/builder.cr

   Line 418 in 3b5bc55

   io.flush

YAML

1. crystal/src/yaml/builder.cr

   Line 67 in 3b5bc55

   @io.flush

2. crystal/src/yaml/builder.cr

   Line 56 in 3b5bc55

   io.flush

Trying to figure out why calling {hello: "world"}.to_json(http_response) is so much slower than http_response.print({hello: "world"}.to_json). This seems like it could be one of the issues since my guess is that the response io would be flushed 3 times per request in the slow version and only once in the quicker. PR updating TechEmpower benchmarks: TechEmpower/FrameworkBenchmarks#6584

I tried referencing other builders but it seems that every one does it differently:

• csv
• xml

[matthewmcgarvey]

Looks like the double flushes were added in this PR #9321 which was made to align the builders flush methods though it didn't remove the old flush calls like it probably should have.

[straight-shoota]

Yeah, I suppose I missed in #9321 that the duplicate flushes should be removed.