Remove 2 corpus tests from GDI suppression list

Corpus tests lines.pdf and 3_alternate.pdf used to fail for Skia
builds with GDI renderer. CL[1] fixed the failures. Therefore remove
the tests from the suppression list.

[1] https://pdfium-review.googlesource.com/111390

Bug: chromium:1474758, pdfium:2056
Change-Id: I579890d3a824bc0bb0f45403bb6f14c0d1788b7e
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/111410
Commit-Queue: Nigi <nigi@chromium.org>
Auto-Submit: Nigi <nigi@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

testing/SUPPRESSIONS

diff --git a/testing/SUPPRESSIONS b/testing/SUPPRESSIONS
index 47b807c..bed3cc1 100644
--- a/testing/SUPPRESSIONS
+++ b/testing/SUPPRESSIONS
@@ -320,7 +320,6 @@
 123.pdf * * * gdi
 1_image.pdf * * * gdi
 2_halftone.pdf * * * gdi
-3_alternate.pdf * * * gdi
 3_interpolate_image.pdf * * * gdi
 3bigpreview.pdf * * * gdi
 4_3.pdf * * * gdi
@@ -408,7 +407,6 @@
 image_jpg.pdf * * * gdi
 image_png.pdf * * * gdi
 image_tif.pdf * * * gdi
-lines.pdf * * * gdi
 mask_array.pdf * * * gdi
 new_stamp2.pdf * * * gdi
 quick_start_guide.pdf * * * gdi