windows/.gitignore: Simplify by removing build artefacts.

Since all output is now in the build-<variant>/ directory, which is already
excluded by the root .gitignore, we don't need to repeat that.

ports/windows/.gitignore

@@ -2,10 +2,6 @@
 *.*sdf
 *.suo
 *.sln
-*.exe
-*.pdb
-*.ilk
 *.filters
-/build/*
 .vs/*
 *.VC.*db