Remove unused routine assert_lacc_equals_i_am_accel_node (!107)

## What is the new feature
`assert_lacc_equals_i_am_accel_node` is not used in ICON any more and should be removed completely.
## How is it implemented
`grep -r assert_lacc_equals_i_am_accel_node` in icon only found the definition and test in libfortran-support.

Co-authored-by: Yen-Chen Chen <yen-chen.chen@kit.edu>
Co-authored-by: Marek Jacob <MeraX@users.noreply.github.com>
Approved-by: Yen-Chen Chen <yen-chen.chen@tum.de>
Merged-by: Yen-Chen Chen <yen-chen.chen@tum.de>
Changelog: feature