Fix gcc warnings in hud/hud.cpp

declaration of ‘render’ shadows a member of 'this'
declaration of ‘font’ shadows a global declaration [-Wshadow]
variable ‘flags’ set but not used [-Wunused-but-set-variable]

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10954 387891d4-d844-0410-90c0-e4c51a9137d3