go/internal/gcimporter: remove skipSpecialPlatforms
go/internal/gcimporter: remove skipSpecialPlatforms

It does not appear to be needed any more.

For golang/go#38415

Change-Id: I5c9525a96606df93c58cc15a4cb4281f95b93902
Reviewed-on: https://go-review.googlesource.com/c/tools/+/360915
Trust: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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