Drop the fit=cover test cases that fill memory without the fix (part of #282)

Without the fix, the 8192x64 and 64x8192 cases each made libvips ask for
about 24 GiB, so a return of the bug would take the build host's memory
instead of failing the test. The cases left fail at once without the fix.

Model: opus-5-5

internal/imageprocessor/fit_cover_internal_test.go

@@ -9,10 +9,10 @@ import (
 )
 
 // TestImageProcessor_FitCoverServesThinSource verifies that FitCover serves
-// a thin source at the requested size. A source of 8192x64 or 8192x1 scaled
+// a thin source at the requested size. An 8192x1 source scaled to cover
-// to cover 8192x8192 is 128 or 8192 times as long as the output on its long
+// 8192x8192 is 8192 times as long as the output on its long side. The centre
-// side. The centre of an 8192x1 source with the proportions of 1x8192 is
+// of an 8192x1 source with the proportions of 1x8192 is 1/8192 of a pixel
-// 1/8192 of a pixel wide. Each case is also turned on its side.
+// wide. Each case is also turned on its side.
 func TestImageProcessor_FitCoverServesThinSource(t *testing.T) {
 	t.Parallel()
 
@@ -21,10 +21,8 @@ func TestImageProcessor_FitCoverServesThinSource(t *testing.T) {
 		inputWidth, inputHeight int
 		size                    Size
 	}{
-		{"8192x64 at 8192x8192", 8192, 64, Size{Width: 8192, Height: 8192}},
 		{"8192x1 at 8192x8192", 8192, 1, Size{Width: 8192, Height: 8192}},
 		{"8192x1 at 1x8192", 8192, 1, Size{Width: 1, Height: 8192}},
-		{"64x8192 at 8192x8192", 64, 8192, Size{Width: 8192, Height: 8192}},
 		{"1x8192 at 8192x8192", 1, 8192, Size{Width: 8192, Height: 8192}},
 		{"1x8192 at 8192x1", 1, 8192, Size{Width: 8192, Height: 1}},
 	}