remove go 1.4.3 from test compilers
remove go 1.4.3 from test compilers

Go 1.5 introduced base64.RawStdEncoding which the ssh library now uses.
So that bumbed up our minimum version to 1.5.

fuchsia-mirror/third_party-github.com-pkg-sftp,fuchsia-mirror/third_party-pkg-sftp,pkg/sftp,ScriptRock/sftp