[SwiftLexicalLookup] Remove some import Foundation

The `import Foundation` seems to not be needed in these two files.
Remove them.

Author: drodriguez

Sources/SwiftLexicalLookup/Configurations/LookupConfig.swift

@@ -10,8 +10,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
-
 @_spi(Experimental) public struct LookupConfig {
   /// Specifies behavior of file scope.
   @_spi(Experimental) public var fileScopeHandling: FileScopeHandlingConfig

Sources/SwiftLexicalLookup/SimpleLookupQueries.swift

@@ -10,7 +10,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
 import SwiftSyntax
 
 extension SyntaxProtocol {