Revert "(CI): added build for c7"

This reverts commit b2244e19.
2 jobs from master in 7 minutes 30 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #5425
rx-build
build and public

04:25

 
  Test
failed #5426
rx-tests
testsuite

03:05

 
Name Stage Failure
failed
testsuite Test
(EE) vboxvideo: module ABI major version (23) doesn't match the server's version (24)
pci id for fd 13: 80ee:beef, driver (null)
(II) modeset(0): Initializing kms color map for depth 24, 8 bpc.
xinit: connection to X server lost

waiting for X server to shut down (II) Server terminated successfully (0). Closing log file.

/home/gitlab-runner/builds/22a11031/0/rx-etersoft/nxssh/rx-testsuite
ERROR: Job failed: exit status 1