Remove Session methods that duplicate DiagCtxt methods.

Also add some `dcx` methods to types that wrap `TyCtxt`, for easier
access.

compiler/rustc_codegen_gcc/src/asm.rs

@@ -109,7 +109,7 @@ enum ConstraintOrRegister {
 impl<'a, 'gcc, 'tcx> AsmBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
     fn codegen_inline_asm(&mut self, template: &[InlineAsmTemplatePiece], rust_operands: &[InlineAsmOperandRef<'tcx, Self>], options: InlineAsmOptions, span: &[Span], instance: Instance<'_>, _dest_catch_funclet: Option<(Self::BasicBlock, Self::BasicBlock, Option<&Self::Funclet>)>) {
         if options.contains(InlineAsmOptions::MAY_UNWIND) {
-            self.sess()
+            self.sess().dcx()
                 .create_err(UnwindingInlineAsm { span: span[0] })
                 .emit();
             return;