Revert "Unify foreign import for vendor:sdl2"

This reverts commit b2b88f1d99.

vendor/sdl2/sdl2.odin

@@ -26,13 +26,11 @@ import "core:c"
 import "core:intrinsics"
 
 when ODIN_OS == .Windows {
-	foreign import _lib "SDL2.lib"
+	foreign import lib "SDL2.lib"
 } else {
-	foreign import _lib "system:SDL2"
+	foreign import lib "system:SDL2"
 }
 
-lib :: _lib
-
 version :: struct {
 	major: u8,        /**< major version */
 	minor: u8,        /**< minor version */
@@ -47,6 +45,7 @@ PATCHLEVEL      :: 16
 foreign lib {
 	GetVersion  :: proc(ver: ^version) ---
 	GetRevision :: proc() -> cstring ---
+
 }
 
 InitFlag :: enum u32 {