Avoid extra cast()s after CStr::as_ptr()

These used to be `&str` literals that did need a pointer cast, but that
became a no-op after switching to `c""` literals in #118566.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -952,7 +952,7 @@ pub fn build_compile_unit_di_node<'ll, 'tcx>(
             producer.as_ptr().cast(),
             producer.len(),
             tcx.sess.opts.optimize != config::OptLevel::No,
-            c"".as_ptr().cast(),
+            c"".as_ptr(),
             0,
             // NB: this doesn't actually have any perceptible effect, it seems. LLVM will instead
             // put the path supplied to `MCSplitDwarfFile` into the debug info of the final