all: fix some go-critic linter warnings

[quasilyte]

     ./accounts/abi/reflect.go:126:3: dupBranchBody: both branches in if statement has same body

It's not a bug, but it looks like it was an attempt to perform some optimization (?)
for structs; when we know it's a struct, we would call setStruct() directly instead
of going through an extra check in set().

Another option would be to remove the branching and use one code for both of them,
the one that calls set() in all cases.

Regexp changes inspired by this warning:

     ./signer/core/validation.go:24:45: badRegexp: suspicious char range `,-.` in [A-Za-z0-9!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~ ]

Accidentally (?) this regexp works as intended, [,-.] is interpreted as a char range,
, is 44, . is 46; so we get a range of 3 chars, [,, char(45), .], it happens
that char(45) is -; but our intentions can be more clearly expressed by enumerating
all 3 characters in a group without a sloppy range, like [,\-.] (note that - is escaped now).

For []rune(t.Type)[0] code we could use utf8.DecodeRuneInString; this avoids the
need to clone string bytes into a fresh []rune just to take the first rune.

A couple of deprecation comments used the non-standard format.
Go tools mostly respect this format: Deprecated: <text>, so
I changed these comments accordingly.

The bw.Cmp(bw) line in tests is clearly a copy/paste mistake quite
common to the tests. Based on the code context, I'm assuming bh should
be used in place of one of the operands.

My personal favorites:

   ./cmd/faucet/faucet.go:744:32: regexpPattern: '.com' should probably be '\.com'
   ./cmd/faucet/faucet.go:870:32: regexpPattern: '.net' should probably be '\.net'

Sometimes we forget to escape . when validation URLs.
This leads to the peculiar effect that allows google.net/ match googlexnet/
which may or may not be a problem (depends on the entire regexp and the context).
go-critic recommends to always escape . in things like .com and .net.

A couple of simple code changes where we simplify the code by calling WriteString(s)
instead of using Write([]byte(s)).

For the benchmark changes, I found these issues:

    ./core/bloombits/generator_test.go:73:4: rangeExprCopy: copy of input (524288 bytes) can be avoided with &input
    ./core/bloombits/generator_test.go:92:4: rangeExprCopy: copy of input (524288 bytes) can be avoided with &input

This is real and Go does copy the array completely, but in this
case the loop body dominates the run time, so copying 0.5mb per benchmark
iteration is not a big deal, but it adds some distortion to the benchmark results.

After changing input to &input I got this diff:

name                old time/op    new time/op    delta
Generator/empty-8     1.00ms ± 2%    0.97ms ± 1%  -3.58%  (p=0.000 n=9+9)
Generator/random-8    30.2ms ± 1%    30.0ms ± 2%    ~     (p=0.065 n=9+10)

It saves ~0.03ms on my machine. It's not a 3.58% speedup, it's a
noise reduced by this amount. Which is good.

[quasilyte]

The failing test is the one that had self-comparison in bw.Cmp(bw).
I would guess that it implies that some other code needs to be fixed.

[holiman]

The \\ is already there, later in the string, [\\]

[quasilyte]

The string is not unescaped, \\ is \, not \\.
So I'm escaping the - to avoid the weird char range; please read the commit message description about it. :)

[holiman]

Doh, rtfm me :)

[holiman]

Can we unescape this too one level and use the backtick operators as the outer delimiters? Seems like it would make things easier

[fjl]

It is not possible to use backquote with this string because it contains the backquote character.

[holiman]

LGTM