Remove the <module>version.h files from .gitignore.

Since e0839abb

 they are created
in the build dir, not the source dir. Further, they are generated
in the include/ dir in the build dir, which is also already ignored
for in-source builds.

Change-Id: I0e709abf4b2b40351eb2728a36e9e238e3fc98bc
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>