[mlir][Transforms][NFC] Dialect conversion: Remove redundant ReplaceBlockArgRewrite (#105963)

There was a redundant `appendRewrite<ReplaceBlockArgRewrite>(block,
origArg);` in `ConversionPatternRewriterImpl::applySignatureConversion`
that had no effect.

Author: matthias-springer

mlir/lib/Transforms/Utils/DialectConversion.cpp

@@ -1296,7 +1296,6 @@ Block *ConversionPatternRewriterImpl::applySignatureConversion(
         OpBuilder::InsertPoint(newBlock, newBlock->begin()), origArg.getLoc(),
         /*inputs=*/replArgs, origArgType, converter);
     mapping.map(origArg, argMat);
-    appendRewrite<ReplaceBlockArgRewrite>(block, origArg);
 
     Type legalOutputType;
     if (converter) {