bulk_add_subscriptions: Fix confusing access to user_profile.realm.
bulk_add_subscriptions: Fix confusing access to user_profile.realm.

Previously, we frequently accessed user_profile.realm from outside the
loops that interact with UserProfile objects.  This variable reuse
outside the loop could be confusing and should be a style/lint
violation.

While in this case, the behavior was correct (in that all users in the
loops were within the same realm), extracting a separate `realm`
variable significantly clarifies what's going on here.

timabbott/zulip,rht/zulip,punchagan/zulip,dhcrzf/zulip,showell/zulip,shubhamdhama/zulip,punchagan/zulip,kou/zulip,tommyip/zulip,synicalsyntax/zulip,zulip/zulip,rishig/zulip,jackrzhang/zulip,kou/zulip,zulip/zulip,rht/zulip,rishig/zulip,showell/zulip,brainwane/zulip,dhcrzf/zulip,kou/zulip,andersk/zulip,andersk/zulip,tommyip/zulip,hackerkid/zulip,kou/zulip,rht/zulip,hackerkid/zulip,tommyip/zulip,zulip/zulip,shubhamdhama/zulip,synicalsyntax/zulip,hackerkid/zulip,dhcrzf/zulip,timabbott/zulip,showell/zulip,zulip/zulip,eeshangarg/zulip,showell/zulip,kou/zulip,shubhamdhama/zulip,eeshangarg/zulip,showell/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,punchagan/zulip,dhcrzf/zulip,timabbott/zulip,rishig/zulip,shubhamdhama/zulip,andersk/zulip,rishig/zulip,punchagan/zulip,synicalsyntax/zulip,showell/zulip,synicalsyntax/zulip,synicalsyntax/zulip,jackrzhang/zulip,eeshangarg/zulip,eeshangarg/zulip,jackrzhang/zulip,kou/zulip,shubhamdhama/zulip,dhcrzf/zulip,zulip/zulip,brainwane/zulip,punchagan/zulip,rht/zulip,hackerkid/zulip,jackrzhang/zulip,zulip/zulip,tommyip/zulip,rht/zulip,jackrzhang/zulip,shubhamdhama/zulip,punchagan/zulip,zulip/zulip,rht/zulip,showell/zulip,andersk/zulip,hackerkid/zulip,tommyip/zulip,rishig/zulip,andersk/zulip,timabbott/zulip,eeshangarg/zulip,tommyip/zulip,jackrzhang/zulip,dhcrzf/zulip,timabbott/zulip,jackrzhang/zulip,synicalsyntax/zulip,eeshangarg/zulip,rishig/zulip,brainwane/zulip,hackerkid/zulip,shubhamdhama/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,rishig/zulip,tommyip/zulip,dhcrzf/zulip,brainwane/zulip,synicalsyntax/zulip,andersk/zulip,kou/zulip,brainwane/zulip,timabbott/zulip,hackerkid/zulip,brainwane/zulip