codegen: Drop unnecessary comma expressions in silent casts
codegen: Drop unnecessary comma expressions in silent casts

Assume temporary variable owns value depending on the relative
expression.

tjol/vala-tjol,flobrosch/vala-fixes,frida/vala,playya/vala,spidermonkdust/vala,jessevdk/vala,spidermonkdust/vala,xdave/pvala,tjol/vala-tjol,Distrotech/vala,jessevdk/vala,rvu95/vala,frida/vala,jessevdk/vala,severinh/vala,flobrosch/vala-fixes,GNOME/vala,flobrosch/vala-fixes,rvu95/vala,spidermonkdust/vala,Distrotech/vala,GNOME/vala,severinh/vala,kamanashisroy/aroop,rvu95/vala,severinh/vala,playya/vala,frida/vala,frida/vala,kamanashisroy/aroop,Distrotech/vala,playya/vala,GNOME/vala,kamanashisroy/aroop,GNOME/vala,tjol/vala-tjol,frida/vala