[NFC] Remove extension macro test from compiler_plugin_basic.swift

(cherry picked from commit 0ac000d)

Author: hborla

lit_tests/compiler_plugin_basic.swift

@@ -34,16 +34,12 @@ macro MemberDeprecated() = #externalMacro(module: "ExamplePlugin", type: "Member
 @attached(conformance)
 macro Equatable() = #externalMacro(module: "ExamplePlugin", type: "EquatableConformanceMacro")
 
-@attached(extension, conformances: Sendable)
-macro AddSendable() = #externalMacro(module: "ExamplePlugin", type: "SendableExtensionMacro")
-
 @attached(accessor)
 macro DidSetPrint() = #externalMacro(module: "ExamplePlugin", type: "DidSetPrintMacro")
 
 @Metadata
 @MemberDeprecated
 @Equatable
-@AddSendable
 @PeerWithSuffix
 struct MyStruct {
   @DidSetPrint
@@ -86,11 +82,6 @@ struct MyStruct {
 // CHECK-NEXT: extension MyStruct : Equatable  {}
 // CHECK-NEXT: ------------------------------
 
-// CHECK: @__swiftmacro_7TestApp8MyStruct9EquatablefMe_.swift
-// CHECK-NEXT: ------------------------------
-// CHECK-NEXT: extension MyStruct: Sendable  {}
-// CHECK-NEXT: ------------------------------
-
 // CHECK: @__swiftmacro_7TestApp8MyStructV5value11DidSetPrintfMa_.swift
 // CHECK-NEXT: ------------------------------
 // CHECK-NEXT: {