Only build and package linux (#30582)

As part of https://github.com/mattermost/mattermost/pull/29932, we
stopped packaging Windows for releases. Let's go one step further and
stop building it too (saves build time!). And while we're in here, stop
doing this for OSX as well.

Both these targets remain buildable on demand, but we don't support
these platforms for production deployments.

server/build/release.mk

@@ -86,9 +86,11 @@ else
 	env GOOS=windows GOARCH=amd64 $(GO) build -o $(GOBIN)/windows_amd64 $(GOFLAGS) -trimpath -tags '$(BUILD_TAGS) production' -ldflags '$(LDFLAGS)' ./cmd/...
 endif
 
-build: setup-go-work build-client build-linux build-windows build-osx
+# Only build linux by default. Other platforms can be built by specifying the platform.
+build: setup-go-work build-client build-linux
 
-build-cmd: setup-go-work build-client build-cmd-linux build-cmd-windows build-cmd-osx
+# Only build linux by default. Other platforms can be built by specifying the platform.
+build-cmd: setup-go-work build-client build-cmd-linux
 
 build-client:
 	@echo Building mattermost web app
@@ -218,6 +220,7 @@ package-windows: package-prep
 	@# Cleanup
 	rm -rf $(DIST_ROOT)/windows
 
-package: package-linux package-osx
+# Only package linux by default. Other platforms can be packaged by specifying the platform.
+package: package-linux
 	rm -rf tmpprepackaged
 	rm -rf $(DIST_PATH)