internal/gomote: remove default create timeout
internal/gomote: remove default create timeout

This change removes the default timeout set for gomote instance
creation. It also cleans up some gomote instance destruction logic.

Updates golang/go#48742

Change-Id: I888142facae23fbb12352c45e3740826b921f61a
Reviewed-on: https://go-review.googlesource.com/c/build/+/374114
Trust: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
Run-TryBot: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Alex Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>

golang/build,golang/build,golang/build,golang/build