cmd/geth, cmd/utils: remove legacy rpc flags (#23358)

* remove rpc flags

* remove legacy rpc flags

* remove legacy rpc flags

* remove legacy rpc commands

* (hopefully) fix most of the build errors

* fix build errors

https://app.travis-ci.com/github/ethereum/go-ethereum/jobs/530318686

* cmd/utils: fix syntax error

* empty commit to unbreak travis ci

* fix syntax error

* syntax fixes

* syntax fixes

* fix

fixes "cmd/geth/usage.go:234:7: expected '(', found init (typecheck)"

* fix

* various fixes in usage.go

* various fixes in flags.go

* adds extra space

reverts the spacing to how it was before I resolved the merge conflict

* more fixes in usage.go

* fix

fix for cmd/geth/usage.go:243:17: expected operand, found ':=' (typecheck) in travis

* Update cmd/utils/flags.go

Co-authored-by: Martin Holst Swende <martin@swende.se>

* fix error

 fixes these errors:
cmd/utils/flags_legacy.go:21:2: "strings" imported but not used (typecheck)

	"strings"

	^

cmd/utils/flags_legacy.go:24:2: "github.com/ethereum/go-ethereum/node" imported but not used (typecheck)

	"github.com/ethereum/go-ethereum/node"

	^

* goimports

Co-authored-by: Martin Holst Swende <martin@swende.se>

cmd/geth/main.go

@@ -158,12 +158,6 @@ var (
 		utils.HTTPPortFlag,
 		utils.HTTPCORSDomainFlag,
 		utils.HTTPVirtualHostsFlag,
-		utils.LegacyRPCEnabledFlag,
-		utils.LegacyRPCListenAddrFlag,
-		utils.LegacyRPCPortFlag,
-		utils.LegacyRPCCORSDomainFlag,
-		utils.LegacyRPCVirtualHostsFlag,
-		utils.LegacyRPCApiFlag,
 		utils.GraphQLEnabledFlag,
 		utils.GraphQLCORSDomainFlag,
 		utils.GraphQLVirtualHostsFlag,