pager: stop using the color extension in tests

The feature is in core so let us use the core config knob directly.

tests/test-pager-legacy.t

@@ -158,8 +158,8 b' Pager should not start if stdout is not '
 Pager with color enabled allows colors to come through by default,
 even though stdout is no longer a tty.
   $ cat >> $HGRCPATH <<EOF
-  > [extensions]
-  > color=
+  > [ui]
+  > color = yes
   > [color]
   > mode = ansi
   > EOF

tests/test-pager.t

@@ -96,8 +96,8 b' be silently lost.)'
 Pager with color enabled allows colors to come through by default,
 even though stdout is no longer a tty.
   $ cat >> $HGRCPATH <<EOF
-  > [extensions]
-  > color=
+  > [ui]
+  > color = yes
   > [color]
   > mode = ansi
   > EOF