release_build_handler: Fix minor warnings reported by pylint

 W: 47,0: Unused import platform
 W: 84,17:BuildJob.__init__: Redefining built-in 'license'
 W:203,65:get_job_list: Redefining name 'platform' from outer scope (line 47)
 W:203,48:get_job_list: Redefining built-in 'license'
 W:282,33:get_repo_job_list: Redefining built-in 'license'
 W:282,50:get_repo_job_list: Redefining name 'platform' from outer scope (line 47)
 W:288,36:get_offline_job_list: Redefining built-in 'license'
 W:288,53:get_offline_job_list: Redefining name 'platform' from outer scope (line 47)
 W:293,35:get_online_job_list: Redefining built-in 'license'
 W:293,52:get_online_job_list: Redefining name 'platform' from outer scope (line 47)
 W:299,45:handle_online_installer_build: Redefining built-in 'license'
 W:299,62:handle_online_installer_build: Redefining name 'platform' from outer scope (line 47)
 W:330,46:handle_offline_installer_build: Redefining built-in 'license'
 W:330,63:handle_offline_installer_build: Redefining name 'platform' from outer scope (line 47)
 W:417,33:handle_repo_build: Redefining built-in 'license'
 W:417,50:handle_repo_build: Redefining name 'platform' from outer scope (line 47)

Change-Id: Ia9ae46cdb0bbed1433cefdc31635b52f94bb5de1
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>