STYLE: Some minor code cleanup in the wrapping setup

The WRAPPER_DO_NOT_CREATE_CXX variable is never used so it was removed.
The macro itk_end_wrap_submodule() is in this case no more needed; instead
call directly the itk_end_wrap_submodule_all_generators() macro.

Remove mention of WRITE_WRAP_CXX in comments; this was an old macro which no more exists,
the writing of the wrap_.cxx.in file is now done in the gccxml generator.

Simplify code for filling up the wrap_.cxx.in file. Intermediate variables were previously used, which is not needed.
Remove @CONFIG_WRAPPER_EXTRAS@ from wrap_.cxx.in file, we are not setting this variable.
Cleaned up the spacing in GCC_XML_TYPEDEFS and  GCC_XML_FORCE_INSTANTIATE for nicer output in .cxx file.

Change-Id: I2806589fdd21e93f08784f472aa13f79e460a1f9
DOC: Fix typo in RelabelComponentImageFilter

Removed also some double spaces.

Change-Id: Ia2d373ca855556e7b2a2ec47365eb52eeea16f5c
Merge topic 'DocTypo'

af1b3fd7 DOC: Fix typo in RelabelComponentImageFilter
Merge topic 'WrapCleanup'

e3964c55 STYLE: Some minor code cleanup in the wrapping setup