Only use one 'END' per file

On visual studio builds the 'END' directive aggressively signals the end
of file.

Change-Id: I28714da32762ef5abcbaeb5a109fb02b80dd13ec

vpx_dsp/arm/variance_media.asm

@@ -152,9 +152,6 @@ loop16x16
 
     ENDP
 
-    END
-
-
 ; r0    unsigned char *src_ptr
 ; r1    int source_stride
 ; r2    unsigned char *ref_ptr
@@ -238,8 +235,6 @@ loop8x8
 
     ENDP
 
-    END
-
 ; r0    unsigned char *src_ptr
 ; r1    int source_stride
 ; r2    unsigned char *ref_ptr