stdlib: remove all FIXME(sil-serialize-all) attributes in StringSwitch.swift

Those attributes were generated automatically, but are not needed.
All the annotated declarations are only used stdlib internally

rdar://problem/45927899

Author: eeckstein

stdlib/public/core/StringSwitch.swift

@@ -39,13 +39,9 @@ struct _OpaqueStringSwitchCache {
   var b: Builtin.Word
 }
 
-@usableFromInline // FIXME(sil-serialize-all)
 internal typealias _StringSwitchCache = Dictionary<String, Int>
 
-@_fixed_layout // FIXME(sil-serialize-all)
-@usableFromInline // FIXME(sil-serialize-all)
 internal struct _StringSwitchContext {
-  @inlinable // FIXME(sil-serialize-all)
   internal init(
     cases: [StaticString],
     cachePtr: UnsafeMutablePointer<_StringSwitchCache>
@@ -54,9 +50,7 @@ internal struct _StringSwitchContext {
     self.cachePtr = cachePtr
   }
 
-  @usableFromInline // FIXME(sil-serialize-all)
   internal let cases: [StaticString]
-  @usableFromInline // FIXME(sil-serialize-all)
   internal let cachePtr: UnsafeMutablePointer<_StringSwitchCache>
 }
 
@@ -94,7 +88,6 @@ func _findStringSwitchCaseWithCache(
 }
 
 /// Builds the string switch case.
-@inlinable // FIXME(sil-serialize-all)
 internal func _createStringTableCache(_ cacheRawPtr: Builtin.RawPointer) {
   let context = UnsafePointer<_StringSwitchContext>(cacheRawPtr).pointee
   var cache = _StringSwitchCache()

test/api-digester/Outputs/stability-stdlib-abi.swift.expected

@@ -81,3 +81,6 @@ Func _makeAnyHashableUpcastingToHashableBaseType(_:storingResultInto:) has been
 
 Func RandomNumberGenerator._fill(bytes:) has been removed
 Func SystemRandomNumberGenerator._fill(bytes:) has been removed
+
+Func _createStringTableCache(_:) has been removed
+Struct _StringSwitchContext has been removed