Revert "Upgrade toolchain to nightly-2025-03-12 (model-checking#3933)"

This reverts commit 44a44e5.

Author: zhassan-aws

kani-compiler/src/codegen_aeneas_llbc/mir_to_ullbc/mod.rs

@@ -813,7 +813,7 @@ impl<'a, 'tcx> Context<'a, 'tcx> {
             let disambiguator = CharonDisambiguator::new(data.disambiguator as usize);
             use rustc_hir::definitions::DefPathData;
             match &data.data {
-                DefPathData::TypeNs(Some(symbol)) => {
+                DefPathData::TypeNs(symbol) => {
                     error_assert!(self, span, data.disambiguator == 0); // Sanity check
                     name.push(CharonPathElem::Ident(symbol.to_string(), disambiguator));
                 }
@@ -956,7 +956,7 @@ impl<'a, 'tcx> Context<'a, 'tcx> {
             let disambiguator = CharonDisambiguator::new(data.disambiguator as usize);
             use rustc_hir::definitions::DefPathData;
             match &data.data {
-                DefPathData::TypeNs(Some(symbol)) => {
+                DefPathData::TypeNs(symbol) => {
                     error_assert!(self, span, data.disambiguator == 0); // Sanity check
                     name.push(CharonPathElem::Ident(symbol.to_string(), disambiguator));
                 }
@@ -1063,7 +1063,7 @@ impl<'a, 'tcx> Context<'a, 'tcx> {
             let disambiguator = CharonDisambiguator::new(data.disambiguator as usize);
             use rustc_hir::definitions::DefPathData;
             match &data.data {
-                DefPathData::TypeNs(Some(symbol)) => {
+                DefPathData::TypeNs(symbol) => {
                     error_assert!(self, span, data.disambiguator == 0); // Sanity check
                     name.push(CharonPathElem::Ident(symbol.to_string(), disambiguator));
                 }

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-03-17"
+channel = "nightly-2025-03-07"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]