Improve //+vet; remove using in many places; add //+vet !using-stmt where necessary

core/image/netpbm/netpbm.odin

@@ -1,3 +1,4 @@
+//+vet !using-stmt
 package netpbm
 
 import "core:bytes"

core/image/png/helpers.odin

@@ -80,11 +80,10 @@ time :: proc(c: image.PNG_Chunk) -> (res: tIME, ok: bool) {
 }
 
 core_time :: proc(c: image.PNG_Chunk) -> (t: coretime.Time, ok: bool) {
-	if png_time, png_ok := time(c); png_ok {
-		using png_time
+	if t, png_ok := time(c); png_ok {
 		return coretime.datetime_to_time(
-			int(year), int(month), int(day),
-			int(hour), int(minute), int(second),
+			int(t.year), int(t.month),  int(t.day),
+			int(t.hour), int(t.minute), int(t.second),
 		)
 	} else {
 		return {}, false

core/image/png/png.odin

@@ -11,6 +11,7 @@
 // package png implements a PNG image reader
 //
 // The PNG specification is at https://www.w3.org/TR/PNG/.
+//+vet !using-stmt
 package png
 
 import "core:compress"
@@ -444,15 +445,14 @@ load_from_context :: proc(ctx: ^$C, options := Options{}, allocator := context.a
 			img.width  = int(header.width)
 			img.height = int(header.height)
 
-			using header
 			h := image.PNG_IHDR{
-				width              = width,
-				height             = height,
-				bit_depth          = bit_depth,
-				color_type         = color_type,
-				compression_method = compression_method,
-				filter_method      = filter_method,
-				interlace_method   = interlace_method,
+				width              = header.width,
+				height             = header.height,
+				bit_depth          = header.bit_depth,
+				color_type         = header.color_type,
+				compression_method = header.compression_method,
+				filter_method      = header.filter_method,
+				interlace_method   = header.interlace_method,
 			}
 			info.header = h