Remove more incorrect os gates (#632)

A lot of logic we have works perfectly fine on other OS'.

Author: dcantah

Sources/Containerization/FileMount.swift

@@ -14,8 +14,6 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
-#if os(macOS)
-
 import ContainerizationError
 import ContainerizationOCI
 import Foundation
@@ -237,5 +235,3 @@ extension FileMountContext {
         }
     }
 }
-
-#endif

Sources/Containerization/LinuxContainer.swift

@@ -14,7 +14,6 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
-#if os(macOS)
 import ContainerizationArchive
 import ContainerizationError
 import ContainerizationExtras
@@ -1288,5 +1287,3 @@ struct IOUtil {
         )
     }
 }
-
-#endif

Sources/Containerization/Mount.swift

@@ -14,10 +14,11 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
-#if os(macOS)
+import ContainerizationError
 import Foundation
+
+#if os(macOS)
 import Virtualization
-import ContainerizationError
 #endif
 
 /// A filesystem mount exposed to a container.