stdlib: Remove #if $NoncopyableGenerics guards.

The stdlib is always built with NoncopyableGenerics enabled, so `#if
$NoncopyableGenerics` guards in non-inlinable code are superfluous.
Additionally, the stdlib's interface no longer needs to support compilers
without the feature, so the guards in inlinable code can also be removed.

Author: tshortli

stdlib/public/core/Bitset.swift

@@ -316,10 +316,8 @@ extension _UnsafeBitset.Word {
 // iterator, not the original word.
 extension _UnsafeBitset.Word: Sequence, IteratorProtocol {
 
-#if $NoncopyableGenerics
   @usableFromInline
   typealias Element = Int
-#endif
 
   @inlinable
   internal var count: Int {

stdlib/public/core/ExistentialCollection.swift

@@ -1286,10 +1286,7 @@ internal struct _ClosureBasedSequence<Iterator: IteratorProtocol> {
 extension _ClosureBasedSequence: Sendable {}
 
 extension _ClosureBasedSequence: Sequence {
-
-#if $NoncopyableGenerics
   public typealias Element = Iterator.Element
-#endif
 
   @inlinable
   internal func makeIterator() -> Iterator {

stdlib/public/core/Misc.swift

@@ -231,7 +231,7 @@ func _rethrowsViaClosure(_ fn: () throws -> ()) rethrows {
 @_marker public protocol Escapable {}
 
 #if $BitwiseCopyable2
-#if $NoncopyableGenerics && $NonescapableTypes
+#if $NonescapableTypes
 @_marker public protocol BitwiseCopyable: ~Escapable { }
 #else
 @_marker public protocol BitwiseCopyable { }
@@ -240,7 +240,7 @@ func _rethrowsViaClosure(_ fn: () throws -> ()) rethrows {
 @available(*, deprecated, message: "Use BitwiseCopyable")
 public typealias _BitwiseCopyable = BitwiseCopyable
 #else
-#if $NoncopyableGenerics && $NonescapableTypes
+#if $NonescapableTypes
 @_marker public protocol _BitwiseCopyable: ~Escapable { }
 #else
 @_marker public protocol _BitwiseCopyable { }

stdlib/public/core/Optional.swift

@@ -230,16 +230,12 @@ extension Optional where Wrapped: ~Copyable {
   public borrowing func _borrowingMap<U: ~Copyable, E: Error>(
     _ transform: (borrowing Wrapped) throws(E) -> U
   ) throws(E) -> U? {
-    #if compiler(>=6.0) && $NoncopyableGenerics
     switch self {
     case .some(let y):
       return .some(try transform(y))
     case .none:
       return .none
     }
-    #else
-    fatalError("unsupported compiler")
-    #endif
   }
 }
 
@@ -308,16 +304,12 @@ extension Optional where Wrapped: ~Copyable {
   public func _borrowingFlatMap<U: ~Copyable, E: Error>(
     _ transform: (borrowing Wrapped) throws(E) -> U?
   ) throws(E) -> U? {
-    #if compiler(>=6.0) && $NoncopyableGenerics
     switch self {
     case .some(let y):
       return try transform(y)
     case .none:
       return .none
     }
-    #else
-    fatalError("Unsupported compiler")
-    #endif
   }
 }
 

stdlib/public/core/Sendable.swift

@@ -132,13 +132,12 @@
 /// ### Sendable Metatypes
 ///
 /// Metatypes such as `Int.Type` implicitly conform to the `Sendable` protocol.
-#if $NoncopyableGenerics && $NonescapableTypes
+#if $NonescapableTypes
 @_marker public protocol Sendable: ~Copyable, ~Escapable { }
-#elseif $NoncopyableGenerics
-@_marker public protocol Sendable: ~Copyable { }
 #else
-@_marker public protocol Sendable { }
+@_marker public protocol Sendable: ~Copyable { }
 #endif
+
 ///
 /// A type whose values can safely be passed across concurrency domains by copying,
 /// but which disables some safety checking at the conformance site.

stdlib/public/core/Sequence.swift

@@ -1272,9 +1272,7 @@ public struct IteratorSequence<Base: IteratorProtocol> {
 
 extension IteratorSequence: IteratorProtocol, Sequence {
 
-  #if $NoncopyableGenerics
-    public typealias Element = Base.Element
-  #endif
+  public typealias Element = Base.Element
 
   /// Advances to the next element and returns it, or `nil` if no next element
   /// exists.