Drop if-return from default ruleset

[rliebz]

The if-return rule was originally a golint rule which was removed from their ruleset for being out of scope. Similarly, it was dropped from revive intentionally as a result of #537. More recently, it was reintroduced into the default ruleset as a result of #799 due to a discrepancy in documentation without a discussion of whether this rule in particular belonged as a part of that default rule set.

While it is no longer a goal of this project to align 100% with the golint defaults, I believe that this rule gives bad advice often enough that it should not be enabled by default.

For example, consider the following code:

if err := func1(); err != nil {
    return err
}

if err := func2(); err != nil {
    return err
}

if err := func3(); err != nil {
    return err
}

return nil

The if-return rule considers this a violation of style, and instead suggests the following:

if err := func1(); err != nil {
    return err
}

if err := func2(); err != nil {
    return err
}

return func3()

While this is more terse, it has a few shortcomings compared to the original. In particular, it means extending the size of the diff if changing the order of checks, adding logic after the call that currently happens to be last, or choosing to wrap the error. And in that last case, it can make it less obvious that there is an unwrapped error being propagated up the call stack.

This in practice has a very similar effect to disabling trailing commas; while it is not necessarily wrong as a style choice, I don't believe it warrants a position as part of the default ruleset here.

See-also: https://github.com/golang/lint/issues/363