gitk: Get rid of the childlist variable
gitk: Get rid of the childlist variable

The information in childlist is a duplicate of what's in the children
array, and it wasn't being accessed often enough to be really worth
keeping the list around as well.

Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git