branch.c: delete size check of newly tracked branch names

Since commit 6f084a56 the length of a newly tracked branch name was limited to 1019 = 1024 - 7 - 7 - 1 characters, a bound derived by having to store this name in a char[1024] called key with two strings of length at most 7 and a '\0' character. This was no longer necessary as of commit a9f2c136, which uses a strbuf (documented in Documentation/technical/api-strbuf.txt) to store this value. Remove this unneeded check to allow branch names longer than 1019 characters. Signed-off-by: Jacopo Notarstefano <jacopo.notarstefano@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>