vcs: fix get_file_annotate - consistently bind sha so it has the right value when executing

The Git implementation did *not* save the sha value in the lambda expression
for the "changeset lazy loader". Thus, if the generator had moved on and
assigned a different value to sha when the expression was executed, it would
use the "wrong" sha.

Fixed by doing as the Hg implementation: bind the sha value as value of a
default parameter when defining the lambda expression.

The Hg implementation did however also save the line - it is not used, and
there is no need for that.