[Gardening] Fix repeated word in diagnostic message

include/swift/AST/DiagnosticsSema.def

@@ -2686,7 +2686,7 @@ ERROR(implementation_only_override_import_without_attr,none,
 // Derived conformances
 ERROR(cannot_synthesize_init_in_extension_of_nonfinal,none,
       "implementation of %0 for non-final class cannot be automatically "
-      "synthesized in extension because initializer requirement %1 can only be "
+      "synthesized in extension because initializer requirement %1 can only "
       "be satisfied by a 'required' initializer in the class definition",
       (Type, DeclName))
 ERROR(cannot_synthesize_in_crossfile_extension,none,

test/decl/protocol/special/coding/class_codable_failure_diagnostics.swift

@@ -112,7 +112,7 @@ class C6 : Codable {
 // Non-final classes cannot synthesize Decodable in an extension.
 class C7 {}
 extension C7 : Decodable {}
-// expected-error@-1 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be be satisfied by a 'required' initializer in the class definition}}
+// expected-error@-1 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be satisfied by a 'required' initializer in the class definition}}
 
 // Check that the diagnostics from an extension end up on the extension
 class C8 {

test/decl/protocol/special/coding/class_codable_simple_conditional.swift

@@ -22,7 +22,7 @@ class Conditional<T> {
 }
 
 extension Conditional: Codable where T: Codable { // expected-note 2 {{where 'T' = 'Nonconforming'}}
-    // expected-error@-1 2 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be be satisfied by a 'required' initializer in the class definition}}
+    // expected-error@-1 2 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be satisfied by a 'required' initializer in the class definition}}
 }
 
 // They should receive synthesized init(from:) and an encode(to:).

test/decl/protocol/special/coding/class_codable_simple_conditional_separate.swift

@@ -25,7 +25,7 @@ extension Conditional: Encodable where T: Encodable { // expected-note {{where '
 }
 
 extension Conditional: Decodable where T: Decodable {
-    // expected-error@-1 2 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be be satisfied by a 'required' initializer in the class definition}}
+    // expected-error@-1 2 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be satisfied by a 'required' initializer in the class definition}}
 }
 
 struct OnlyEnc: Encodable {}

test/decl/protocol/special/coding/class_codable_simple_extension.swift

@@ -20,7 +20,7 @@ class SimpleClass { // expected-note {{did you mean 'init'?}}
   }
 }
 
-extension SimpleClass : Codable {} // expected-error 2 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be be satisfied by a 'required' initializer in the class definition}}
+extension SimpleClass : Codable {} // expected-error 2 {{implementation of 'Decodable' for non-final class cannot be automatically synthesized in extension because initializer requirement 'init(from:)' can only be satisfied by a 'required' initializer in the class definition}}
 
 // They should not receive synthesized init(from:), but should receive an encode(to:).
 let _ = SimpleClass.init(from:) // expected-error {{type 'SimpleClass' has no member 'init(from:)'}}