Remove get_host_triple() from install-template.sh
Remove get_host_triple() from install-template.sh

Rather than adding SunOS/Solaris (or any future supported OSes) to
`get_host_triple()`'s list of known OSes, recognize that the function is
called in exactly two places, and both times the only thing that matters
is whether it's Linux or not.

rust-lang/rust-installer,rust-lang/rust-installer