Use rustc_fluent_macro::fluent_messages! directly.

Currently we always do this:
```
use rustc_fluent_macro::fluent_messages;
...
fluent_messages! { "./example.ftl" }
```
But there is no need, we can just do this everywhere:
```
rustc_fluent_macro::fluent_messages! { "./example.ftl" }
```
which is shorter.

compiler/rustc_resolve/src/lib.rs

@@ -40,7 +40,6 @@ use rustc_data_structures::sync::{FreezeReadGuard, Lrc};
 use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_expand::base::{DeriveResolutions, SyntaxExtension, SyntaxExtensionKind};
 use rustc_feature::BUILTIN_ATTRIBUTES;
-use rustc_fluent_macro::fluent_messages;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::NonMacroAttrKind;
 use rustc_hir::def::{self, CtorOf, DefKind, DocLinkResMap, LifetimeRes, PartialRes, PerNS};
@@ -88,7 +87,7 @@ mod late;
 mod macros;
 pub mod rustdoc;
 
-fluent_messages! { "../messages.ftl" }
+rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 
 #[derive(Debug)]
 enum Weak {