Revert "OpenMP/OpenACC tests. vs C++26"

This reverts commit edc821b60ce94b8ddb5d0b9ccdb9a0a4691371c7.

With -std=c++26 (-freflections), [: and :] are tokenized as open/close splice
instead of open/close square bracket - which caused parser issues for OpenMP
and OpenACC array sections of the form '[ lower : size ]' when specified
without lower or size; especially, usage like '[:N]' is ubiquitous.

To permit compilation with -std=c++26, commit r16-5330-gedc821b60ce94b added
a space between colon and bracket. However, since
  commit r17-2993-g8f43cf55107e34
  C++: Handle OpenMP/OpenACC array sections [: / :] with C++26
the extra space is no longer required such that the commit could be reverted.