The primary improvement is in early clearing of
analyzed package's TypeInfo, facts, etc for
whole program analyzers (`unused`). Clear it when it
becomes unused and GC collects them early. Initially this
clearing was performed for all analyzers except `unused`.
Update staticcheck from v0.0.1-2019.2.3 to v0.0.1-2020.1.4
Also in this commit:
* speed up loading packages from export data (2.5s -> 2.1s for std)
by not using mutex for export data since it was allowed in
x/tools#07722704da13
* make an order of execution of linters stable
* update renameio and robustio
* use robustio in caching
Relates: #987, #994, #995, #1011
