Remove range-metadata amdgpu workaround

Range metadata was disabled for amdgpu due to a backend bug. I did not
encounter any problems when removing the workaround to enable range
metadata (tried compiling `core` and `alloc`), so I assume this has
been fixed in LLVM in the last years.

Remove the workaround to re-enable range metadata.

compiler/rustc_codegen_llvm/src/builder.rs

@@ -610,14 +610,6 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
     }
 
     fn range_metadata(&mut self, load: &'ll Value, range: WrappingRange) {
-        if self.sess().target.arch == "amdgpu" {
-            // amdgpu/LLVM does something weird and thinks an i64 value is
-            // split into a v2i32, halving the bitwidth LLVM expects,
-            // tripping an assertion. So, for now, just disable this
-            // optimization.
-            return;
-        }
-
         if self.cx.sess().opts.optimize == OptLevel::No {
             // Don't emit metadata we're not going to use
             return;