internal/lsp: remove nilness analyzer
internal/lsp: remove nilness analyzer

The nilness analyzer requires SSA, which is very expensive to build and
uses a lot of RAM. It also seems to really shoot up memory usage when it
hits certain cases, which is causing a lot of problems for users.
Disable this analysis - we'll leave SSA to staticcheck.

Updates golang/go#36639

Change-Id: I46e67a6fd7828a5fddcd42d1aa00876f17c79e3d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/219203
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools