chainlint.sed: drop unnecessary distinction between ?!AMP?! and ?!SEMI?!

chainlint.sed: drop unnecessary distinction between ?!AMP?! and ?!SEMI?!

>From inception, when chainlint.sed encountered a line using semicolon to
separate commands rather than `&&`, it would insert a ?!SEMI?!
annotation at the beginning of the line rather ?!AMP?! even though the
&&-chain is also broken by the semicolon. Given a line such as:

    ?!SEMI?! cmd1; cmd2 &&

the ?!SEMI?! annotation makes it easier to see what the problem is than
if the output had been:

    ?!AMP?! cmd1; cmd2 &&

which might confuse the test author into thinking that the linter is
broken (since the line clearly ends with `&&`).

However, now that the ?!AMP?! an ?!SEMI?! annotations are inserted at
the point of breakage rather than at the beginning of the line, and
taking into account that both represent a broken &&-chain, there is
little reason to distinguish between the two. Using ?!AMP?! alone is
sufficient to point the test author at the problem. For instance, in:

    cmd1; ?!AMP?! cmd2 &&
    cmd3

it is clear that the &&-chain is broken between `cmd1` and `cmd2`.
Likewise, in:

    cmd1 && cmd2 ?!AMP?!
    cmd3

it is clear that the &&-chain is broken between `cmd2` and `cmd3`.
Finally, in:

    cmd1; ?!AMP?! cmd2 ?!AMP?!
    cmd3

it is clear that the &&-chain is broken between each command.

Hence, there is no longer a good reason to make a distinction between a
broken &&-chain due to a semicolon and a broken chain due to a missing
`&&` at end-of-line. Therefore, drop the ?!SEMI?! annotation and use
?!AMP?! exclusively.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>