docs: remove stray bracket from git-clone synopsis

docs: remove stray bracket from git-clone synopsis

The synopsis section has an extra closing bracket, like this:

    [--filter=<filter>] [--also-filter-submodules]]

The extra one is not the one at the end of this line; it is the one
after "...=<filter>".

The "--also-filter-submodules" option was added by f05da2b4 (clone,
submodule: pass partial clone filters to submodules, 2022-02-04).
Because it makes sense only when used with the "--filter=<filter>"
option, these two options are enclosed in a pair of brackets.  The
extra one was added by 76880f05 (doc: git-clone: apply new
documentation formatting guidelines, 2024-03-29) by mistake.

Remove the extra and incorrect closing bracket, so that the line
reads:

    [--filter=<filter> [--also-filter-submodules]]

Signed-off-by: Knut Harald Ryager <e-k-nut@hotmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>