sequencer: remove unnecessary variable setting

revs.pretty_given is only ever used in builtin/log.c, which is never
called from sequencer.  So setting this variable cannot do anything.
Remove it.

This was introduced in commit 62db524 ("rebase -i: generate the
script via rebase--helper", 2017-07-14), which was converting from a
literal usage of log, which suggests this line was copied or ported
from log.c even though it has no use here.

Author: newren

sequencer.c

@@ -6086,7 +6086,6 @@ int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
 	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
 	revs.topo_order = 1;
 
-	revs.pretty_given = 1;
 	git_config_get_string("rebase.instructionFormat", &format);
 	if (!format || !*format) {
 		free(format);