[Macros] Remove MacroSystem and related files from 'SwiftSyntaxMacros'

All the users of "MacroSystem" in `SwiftSyntaxMacros` have migrated to
`SwiftSyntaxMacroExpansion`. Remove `MacroSystem.swift` and related
files from `SwiftSyntaxMacros` module.

rdar://111588860

Author: rintaro

Package.swift

@@ -178,14 +178,6 @@ let package = Package(
       exclude: ["CMakeLists.txt"]
     ),
 
-    .testTarget(
-      name: "SwiftSyntaxMacrosTest",
-      dependencies: [
-        "_SwiftSyntaxTestSupport", "SwiftDiagnostics", "SwiftOperators", "SwiftParser", "SwiftSyntaxBuilder", "SwiftSyntaxMacros",
-        "SwiftSyntaxMacrosTestSupport",
-      ]
-    ),
-
     // MARK: SwiftSyntaxMacroExpansion
 
     .target(
@@ -196,7 +188,10 @@ let package = Package(
 
     .testTarget(
       name: "SwiftSyntaxMacroExpansionTest",
-      dependencies: ["SwiftSyntax", "_SwiftSyntaxTestSupport", "SwiftSyntaxMacroExpansion", "SwiftSyntaxBuilder"]
+      dependencies: [
+        "SwiftSyntax", "_SwiftSyntaxTestSupport", "SwiftDiagnostics", "SwiftOperators", "SwiftParser", "SwiftSyntaxBuilder", "SwiftSyntaxMacros",
+        "SwiftSyntaxMacroExpansion", "SwiftSyntaxMacrosTestSupport",
+      ]
     ),
 
     // MARK: SwiftSyntaxMacrosTestSupport

Sources/SwiftSyntaxMacros/BasicMacroExpansionContext.swift

@@ -22,13 +22,9 @@ add_swift_host_library(SwiftSyntaxMacros
   MacroProtocols/PeerMacro.swift
 
   AbstractSourceLocation.swift
-  BasicMacroExpansionContext.swift
   MacroExpansionContext.swift
-  MacroSystem.swift
-  Syntax+MacroEvaluation.swift
 )
 
 target_link_libraries(SwiftSyntaxMacros PUBLIC
-  SwiftParser
   SwiftSyntaxBuilder
   )

Sources/SwiftSyntaxMacros/CMakeLists.txt

@@ -12,7 +12,6 @@
 
 import SwiftDiagnostics
 import SwiftSyntax
-import SwiftSyntaxBuilder
 
 /// Interface to extract information about the context in which a given
 /// macro is expanded.