Repo.vim: use correct variable

After one of the recent changes 'deleted' was used in a place where
'removed' should have been used. This could lead errors:

Error detected while processing function
   sy#toggle..sy#start..sy#repo#process_diff..sy#sign#set:
line   10:
E155: Unknown sign: SignifyChangeDelete12
Merge pull request 78 from esneider

Closes #78.