Remove redundant Equatable conformances in code generation (#214)

### Motivation

Fixes #210.

### Modifications

With this PR. we are removing the explicit `Equatable` conformance when
a type already conforms to `Hashable`
 in generated code.

### Result

Generated types now conforms explicitly to `Hashable` but not to
`Equatable`.

```diff
- public struct Generated: Equatable, Hashable {
  }
+ public sutrct Generated: Hashable {
 }
```

### Test Plan

I have updated the reference ressources used by tests to check generated
code.

Sources/_OpenAPIGeneratorCore/FeatureFlags.swift

@@ -25,7 +25,7 @@
 /// enabled unconditionally on main and the feature flag removed, and version
 /// 0.2 is tagged. (This is for pre-1.0 versioning, would be 1.0 and 2.0 after
 /// 1.0 is released.)
-public enum FeatureFlag: String, Hashable, Equatable, Codable, CaseIterable {
+public enum FeatureFlag: String, Hashable, Codable, CaseIterable {
 
     /// Multiple request and response body content types.
     ///

Sources/_OpenAPIGeneratorCore/Translator/CommonTypes/Constants.swift

@@ -127,7 +127,6 @@ enum Constants {
         /// The types that every struct conforms to.
         static let conformances: [String] = [
             "Codable",
-            "Equatable",
             "Hashable",
             "Sendable",
         ]
@@ -154,7 +153,6 @@ enum Constants {
         /// The types that every enum conforms to.
         static let conformances: [String] = [
             "Codable",
-            "Equatable",
             "Hashable",
             "Sendable",
             "_AutoLosslessStringConvertible",
@@ -208,7 +206,6 @@ enum Constants {
             /// The types that the body conforms to.
             static let conformances: [String] = [
                 "Sendable",
-                "Equatable",
                 "Hashable",
             ]
         }
@@ -225,7 +222,6 @@ enum Constants {
             /// The types that the Input type conforms to.
             static let conformances: [String] = [
                 "Sendable",
-                "Equatable",
                 "Hashable",
             ]
         }
@@ -239,7 +235,6 @@ enum Constants {
             /// The types that the Output type conforms to.
             static let conformances: [String] = [
                 "Sendable",
-                "Equatable",
                 "Hashable",
             ]
 
@@ -249,7 +244,6 @@ enum Constants {
                 /// The types that the Payload type conforms to.
                 static let conformances: [String] = [
                     "Sendable",
-                    "Equatable",
                     "Hashable",
                 ]
 
@@ -272,7 +266,6 @@ enum Constants {
                     /// The types that the Headers type conforms to.
                     static let conformances: [String] = [
                         "Sendable",
-                        "Equatable",
                         "Hashable",
                     ]
                 }

Sources/_OpenAPIGeneratorCore/Translator/Content/CodingStrategy.swift

@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 /// Describes the underlying coding strategy.
-enum CodingStrategy: String, Equatable, Hashable, Sendable {
+enum CodingStrategy: String, Hashable, Sendable {
 
     /// A strategy using JSONEncoder/JSONDecoder.
     case json

Tests/OpenAPIGeneratorReferenceTests/FileBasedReferenceTests.swift

@@ -146,7 +146,7 @@ class FileBasedReferenceTests: XCTestCase {
         }
     }
 
-    struct ReferenceProject: Hashable, Equatable {
+    struct ReferenceProject: Hashable {
         var name: ReferenceProjectName
         var customDirectoryName: String? = nil