remove "//go:build go1.26" workarounds

These were added because the repository was not a module: consumers
got an implicitly generated go.mod, which made go assume the "go1.16"
language version and reject any newer language feature. The "//go:build"
directive overrode the language version on a per-file basis.

Now that there is a real go.mod, its "go" directive sets the language
version for every file in the module, so the workaround can go, as the
FIXME they carried asked for.

Assisted-by: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

Author: AkihiroSuda

cli-plugins/hooks/hook_types.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 // Package hooks defines the contract between the Docker CLI and CLI plugin hook
 // implementations.
 //

cli-plugins/hooks/template.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package hooks
 
 import (

cli-plugins/manager/error.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package manager
 
 import (

cli-plugins/manager/hooks.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package manager
 
 import (

cli-plugins/manager/manager.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package manager
 
 import (

cli-plugins/manager/plugin.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package manager
 
 import (

cli-plugins/plugin/plugin.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package plugin
 
 import (

cli/cobra.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package cli
 
 import (

cli/command/cli.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package command
 
 import (

cli/command/config/formatter.go

@@ -1,6 +1,3 @@
-// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
-//go:build go1.26
-
 package config
 
 import (