message: Remove usage of always empty writable in `JsonParserGenerator`
  The writable calculates a string that it never writes.
  This was added in
diff: @@ -35,7 +35,6 @@ import software.amazon.smithy.rust.codegen.core.rustlang.rustBlockTemplate
  import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
  import software.amazon.smithy.rust.codegen.core.rustlang.withBlock
  import software.amazon.smithy.rust.codegen.core.rustlang.withBlockTemplate
  -import software.amazon.smithy.rust.codegen.core.rustlang.writable
  import software.amazon.smithy.rust.codegen.core.smithy.CodegenContext
  import software.amazon.smithy.rust.codegen.core.smithy.CodegenTarget
  import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
  @@ -51,7 +50,6 @@ import software.amazon.smithy.rust.codegen.core.smithy.isRustBoxed
  import software.amazon.smithy.rust.codegen.core.smithy.protocols.HttpBindingResolver
  import software.amazon.smithy.rust.codegen.core.smithy.protocols.HttpLocation
  import software.amazon.smithy.rust.codegen.core.smithy.protocols.deserializeFunctionName
  -import software.amazon.smithy.rust.codegen.core.smithy.rustType
  import software.amazon.smithy.rust.codegen.core.util.PANIC
  import software.amazon.smithy.rust.codegen.core.util.dq
  import software.amazon.smithy.rust.codegen.core.util.hasTrait
  @@ -298,8 +296,7 @@ class JsonParserGenerator(
  private fun RustWriter.deserializeBlob(target: BlobShape) {
  rustTemplate(
  - "#{expect_blob_or_null}(tokens.next())?#{ConvertFrom:W}",
  - "ConvertFrom" to writable { RuntimeType.blob(runtimeConfig).toSymbol().rustType().render() },
  + "#{expect_blob_or_null}(tokens.next())?",
  *codegenScope,
  )
  }
  