Revert "Use HintFmt for doc comments"

Unfortunately these don't render correctly, because they go into the
markdown renderer, instead of the terminal.

```
nix-repl> :doc lib.version
Attribute '[35;1mversion[0m'

    … defined at [35;1m/home/user/h/nixpkgs/lib/default.nix:73:40[0m
```

We could switch that to go direct to the terminal, but then we should
do the same for the primops, to get a consistent look.

Reverting for now.

This reverts commit 3413e0338cbee1c7734d5cb614b5325e51815cde.

src/libcmd/repl.cc

@@ -668,12 +668,12 @@ ProcessLineResult NixRepl::processLine(std::string line)
             logger->cout(trim(renderMarkdownToTerminal(markdown)));
         } else if (fallbackPos) {
             std::stringstream ss;
-            ss << HintFmt("Attribute '%1%'", fallbackName) << "\n\n";
-            ss << HintFmt("  … defined at %1%", state->positions[fallbackPos]) << "\n\n";
+            ss << "Attribute `" << fallbackName << "`\n\n";
+            ss << "  … defined at " << state->positions[fallbackPos] << "\n\n";
             if (fallbackDoc) {
                 ss << fallbackDoc.getInnerText(state->positions);
             } else {
-                ss << HintFmt("No documentation found.") << "\n\n";
+                ss << "No documentation found.\n\n";
             }
 
             auto markdown = ss.str();

src/libexpr/eval.cc

@@ -576,17 +576,17 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
         }
 
         if (name.empty()) {
-            s << HintFmt("Function ");
+            s << "Function ";
         }
         else {
-            s << HintFmt("Function '%s'", name);
+            s << "Function `" << name << "`";
             if (pos)
                 s << "\\\n  … " ;
             else
                 s << "\\\n";
         }
         if (pos) {
-            s << HintFmt("defined at %1%", pos);
+            s << "defined at " << pos;
         }
         if (!docStr.empty()) {
             s << "\n\n";