docs: fix stale references in resolver and parser comments and the prqlc-c README

[prql-bot]

Fixes three references that point at things that no longer exist. Comments and docs only; no code changes.

• prqlc/bindings/prqlc-c/README.md. The README said the Zig example uses @cImport. Since ci: update minimal-zig example to the Zig 0.17 build API #6402 it translates prqlc.h with b.addTranslateC in build.zig, and src/main.zig does @import("prqlc").
• Resolver::in_func_call_name (semantic/resolver/mod.rs). The doc comment linked [test::test_func_call_resolve], which doesn't exist anywhere in the workspace. It now says what the flag does: resolver/expr.rs sets it while folding a call's name, so a function decl is returned as-is instead of going through fold_expr.
• prqlc-parser/src/parser/pr/expr.rs. A comment said the code below it "is tested by the tests_misc crate to match expr.rs in prqlc". No tests_misc crate exists any more, so the comment is removed.

These came from the nightly review of recent commits (#6402) and the rolling file survey. No test applies, and they don't need a changelog entry.