test: Update ref output

PRs 4840 and 4841 crossed in flight with their tests passing
individually, but they needed one small adjustment to reference output
to account for their interaction.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

testsuite/maketx/ref/out-alt.txt

@@ -337,7 +337,6 @@ nan.exr              :   64 x   64, 3 channel, half openexr
     textureformat: "Plain Texture"
     wrapmodes: "black,black"
     oiio:AverageColor: "0.5,0.5,0.5"
-    oiio:ColorSpace: "lin_rec709"
     oiio:SHA-1: "44B96A7C3AFBF8D7621E7C6453266E5DD1962D36"
     oiio:subimages: 1
     openexr:levelmode: 0
@@ -366,7 +365,6 @@ checker-exr.pdq      :  128 x  128, 4 channel, half openexr
     textureformat: "Plain Texture"
     wrapmodes: "black,black"
     oiio:AverageColor: "0.5,0.5,0.5,1"
-    oiio:ColorSpace: "lin_rec709"
     oiio:SHA-1: "D924CA144A02479D1507F5910F5FC8F51EF78765"
     oiio:subimages: 1
     openexr:lineOrder: "increasingY"