software/slapos-sr-testing: run repman only on python3

in ceb063a4 (software/repman: tests python3 compliance, 2020-10-23), test
profile was changed to run on python3 only but this was accidentally
reverted in 3a1e5628 (software/slapos-sr-testing: use nxdtest, 2020-10-28),
by running repman also on python2.

Restore the situation where we run repman only on python3

software/slapos-sr-testing/software.cfg

@@ -271,7 +271,6 @@ extra =
   gitlab ${slapos.test.gitlab-setup:setup}
   cloudooo ${slapos.test.cloudooo-setup:setup}
   dream ${slapos.test.dream-setup:setup}
-  repman ${slapos.test.repman-setup:setup}
 
 [versions]
 # slapos.core is used from the clone always