TUN-3964: Revert "TUN-3922: Repoint urfave/cli/v2 library at patched branch at github.com/ipostelnik/cli/v2@fixed which correctly handles reading flags declared at multiple levels of subcommands."

This reverts commit 1670ee87fb.

vendor/github.com/urfave/cli/v2/altsrc/fg.py

@@ -1,45 +0,0 @@
-# Only types that provide implementation of FlagInputSourceExtension can be listed here
-# please keep list sorted alphabetically
-flag_types = [
-    "Bool",
-    "Duration",
-    "Float64",
-    "Generic",
-    "Int",
-    "IntSlice",
-    "Path",
-    "String",
-    "StringSlice",
-]
-
-print('''// Code generated by fg.py; DO NOT EDIT.
-
-package altsrc
-
-import (
-	"flag"
-
-	"github.com/urfave/cli/v2"
-)''')
-
-for t in flag_types:
-    print(f'''
-// {t}Flag is the flag type that wraps cli.{t}Flag to allow
-// for other values to be specified
-type {t}Flag struct {{
-	*cli.{t}Flag
-	set *flag.FlagSet
-}}
-var _ FlagInputSourceExtension = (*{t}Flag)(nil)
-
-// New{t}Flag creates a new {t}Flag
-func New{t}Flag(fl *cli.{t}Flag) *{t}Flag {{
-	return &{t}Flag{{{t}Flag: fl, set: nil}}
-}}
-
-// Apply saves the flagSet for later usage calls, then calls
-// the wrapped {t}Flag.Apply
-func (f *{t}Flag) Apply(set *flag.FlagSet) error {{
-	f.set = set
-	return f.{t}Flag.Apply(set)
-}}''')