Remove 'ignore = all' from .gitmodules

I would like to see the changes in git status.

Change-Id: I5b97af3cd467639aa4df1bcfd717f33c5b820c4b
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

.gitmodules

 [submodule "src/3rdparty"]
     path = src/3rdparty
     url = ../qtwebengine-chromium.git
-    ignore = all
+    ignore = dirty
     initrepo = true