Revert "[mlir][arith] Refine the verifier for arith.constant (#86178)"

This reverts commit 662c626.

Broken both:
  * https://lab.llvm.org/buildbot/#/builders/61/builds/56565

Author: banach-space

mlir/lib/Dialect/Arith/IR/ArithOps.cpp

@@ -213,12 +213,6 @@ LogicalResult arith::ConstantOp::verify() {
     return emitOpError(
         "value must be an integer, float, or elements attribute");
   }
-
-  auto vecType = dyn_cast<VectorType>(type);
-  if (vecType && vecType.isScalable() && !isa<SplatElementsAttr>(getValue()))
-    return emitOpError(
-        "intializing scalable vectors with elements attribute is not supported"
-        " unless it's a vector splat");
   return success();
 }
 

mlir/test/Dialect/Arith/invalid.mlir

@@ -64,15 +64,6 @@ func.func @constant_out_of_range() {
 
 // -----
 
-func.func @constant_invalid_scalable_vec_initialization() {
-^bb0:
-  // expected-error@+1 {{'arith.constant' op intializing scalable vectors with elements attribute is not supported unless it's a vector splat}}
-  %c = arith.constant dense<[0, 1]> : vector<[2] x i32>
-  return
-}
-
-// -----
-
 func.func @constant_wrong_type() {
 ^bb:
   %x = "arith.constant"(){value = 10.} : () -> f32 // expected-error {{'arith.constant' op failed to verify that all of {value, result} have same type}}