internal/lsp/cache: remove parseGo semaphore
internal/lsp/cache: remove parseGo semaphore

The original intention was to limit the number of open file handles,
but the parseLimit semaphore was limiting parser.ParseFile calls that
don't access files, so there was no benefit. The file limiting is
already handled generically by another semaphore in the lsp FileSystem
abstraction.

Change-Id: Idc7f2507af5287e983a7edf3e38a848d26770bbe
Reviewed-on: https://go-review.googlesource.com/c/tools/+/223119
Run-TryBot: Muir Manders <f51fb43e34cc3dd13703253fda59ef2c5e0b683b@mnd.rs>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

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