Replace target.target with target and target.ptr_width with target.pointer_width

Preparation for a subsequent change that replaces
rustc_target::config::Config with its wrapped Target.

On its own, this commit breaks the build. I don't like making
build-breaking commits, but in this instance I believe that it
makes review easier, as the "real" changes of this PR can be
seen much more easily.

Result of running:

find compiler/ -type f -exec sed -i -e 's/target\.target\([)\.,; ]\)/target\1/g' {} \;
find compiler/ -type f -exec sed -i -e 's/target\.target$/target/g' {} \;
find compiler/ -type f -exec sed -i -e 's/target.ptr_width/target.pointer_width/g' {} \;
./x.py fmt

compiler/rustc_symbol_mangling/src/lib.rs

@@ -201,7 +201,7 @@ fn compute_symbol_name(
     //
     // [1]: https://bugs.llvm.org/show_bug.cgi?id=44316
     if is_foreign {
-        if tcx.sess.target.target.arch != "wasm32"
+        if tcx.sess.target.arch != "wasm32"
             || !tcx.wasm_import_module_map(def_id.krate).contains_key(&def_id)
         {
             if let Some(name) = attrs.link_name {