go: remove support for GOROOT_FINAL

go: remove support for GOROOT_FINAL

After upstream go applied commit [cmd: remove support for
GOROOT_FINAL][1], GOROOT_FINAL variable is dropped and use
option -trimpath to instead [2]

The option -trimpath has already been added to GOBUILDFLAGS
in go.bbclass

[1] https://github.com/golang/go/commit/507d1b22f4b58ac68841582d0c2c0ab6b20e5a98
[2] https://github.com/golang/go/issues/62047

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>