Remove usage of always empty writable in JsonParserGenerator (#2192)

The writable calculates a string that it never writes.

This was added in #2131.

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/JsonParserGenerator.kt

@@ -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,
         )
     }