Rollup merge of #151887 - scottmcm:homogeneous-try-in-compiler, r=jackh726

Remove some unnecessary `try`-related type annotations

I left a few, like
```rust
let result: Result<_, ModError<'_>> = try {
```
where it felt like seeing it might still be useful for the reader.

Feel free to push back on any of these changes if you think they should be left alone.

compiler/rustc_borrowck/src/nll.rs

@@ -231,13 +231,13 @@ pub(super) fn dump_nll_mir<'tcx>(
     dumper.dump_mir(body);
 
     // Also dump the region constraint graph as a graphviz file.
-    let _: io::Result<()> = try {
+    let _ = try {
         let mut file = dumper.create_dump_file("regioncx.all.dot", body)?;
         regioncx.dump_graphviz_raw_constraints(tcx, &mut file)?;
     };
 
     // Also dump the region constraint SCC graph as a graphviz file.
-    let _: io::Result<()> = try {
+    let _ = try {
         let mut file = dumper.create_dump_file("regioncx.scc.dot", body)?;
         regioncx.dump_graphviz_scc_constraints(tcx, &mut file)?;
     };

compiler/rustc_borrowck/src/polonius/dump.rs

@@ -58,7 +58,7 @@ pub(crate) fn dump_polonius_mir<'tcx>(
 
     let dumper = dumper.set_extra_data(extra_data).set_options(options);
 
-    let _: io::Result<()> = try {
+    let _ = try {
         let mut file = dumper.create_dump_file("html", body)?;
         emit_polonius_dump(
             &dumper,