Remove number from operator mismatch message.

pkg/front_end/messages.yaml

Index: pkg/front_end/messages.yaml
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index 99f9f44e22f9febf5d704b5b0fed30da3d5bf5ea..55bf16a644d037b4c52ca92916d1a0adfaa102a2 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -46,8 +46,6 @@
 #
 # `#name2` another name (a string).
 #
-# `#number` a number (an integer).
-#
 # `#lexeme` a token. The token's `lexeme` property is used.
 #
 # `#string` a string.
@@ -766,8 +764,14 @@ DuplicatedParameterNameCause:
 EnumConstantSameNameAsEnclosing:
   template: "Name of enum constant '#name' can't be the same as the enum's own name."
 
-OperatorParameterMismatch:
-  template: "Operator '#name' must have exactly #number parameters."
+OperatorParameterMismatch0:
+  template: "Operator '#name' shouldn't have any parameters."
+
+OperatorParameterMismatch1:
+  template: "Operator '#name' should have exactly one parameter."
+
+OperatorParameterMismatch2:
+  template: "Operator '#name' should have exactly two parameters."
 
 SupertypeIsIllegal:
   template: "The type '#name' can't be used as supertype."