Remove trait CoverageInfoMethods, since non-LLVM backends don't need it

These methods are only ever called from within `rustc_codegen_llvm`, so they
can just be declared there as well.

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -4,7 +4,7 @@ use crate::llvm;
 
 use llvm::coverageinfo::CounterMappingRegion;
 use rustc_codegen_ssa::coverageinfo::map::{Counter, CounterExpression};
-use rustc_codegen_ssa::traits::{ConstMethods, CoverageInfoMethods};
+use rustc_codegen_ssa::traits::ConstMethods;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;