Revert "[gitignore] added Makefile.in"

This reverts commit 1506cc6360c63591626658ff4198b3fefc3ce65b.

Conflicts:

	.gitignore

Reverted because configure does not succeed anymore:
...
configure: creating ./config.status
config.status: creating Makefile
config.status: creating dune/Makefile
config.status: creating dune/stuff/Makefile
config.status: creating dune/stuff/common/Makefile
config.status: creating dune/stuff/fem/Makefile
config.status: creating dune/stuff/fem/functions/Makefile
config.status: creating dune/stuff/function/Makefile
config.status: creating dune/stuff/grid/Makefile
config.status: creating dune/stuff/grid/provider/Makefile
config.status: creating dune/stuff/grid/output/Makefile
config.status: creating dune/stuff/projection/Makefile
config.status: creating dune/stuff/test/Makefile
config.status: error: cannot find input file: `dune/stuff/test/gtest/Makefile.in'
...

.gitignore

@@ -39,6 +39,5 @@ am
 CMakeLists.txt.user
 demos
 *.gch
-Makefile.in
 *.lo
 dune/stuff/test/gtest/lib