internal/rosa: respect preferred job count

This discontinues use of nproc, and also overrides detection behaviour in ninja.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/curl.go

@@ -15,7 +15,7 @@ func (t Toolchain) newCurl() (pkg.Artifact, string) {
 		// remove broken test
 		Writable: true,
 		ScriptEarly: `
-chmod +w tests/data && rm tests/data/test459
+chmod +w tests/data && rm -f tests/data/test459
 `,
 	}, &MakeHelper{
 		Configure: []KV{
@@ -25,7 +25,7 @@ chmod +w tests/data && rm tests/data/test459
 			{"disable-smb"},
 		},
 		Check: []string{
-			`TFLAGS="-j$(expr "$(nproc)" '*' 2)"`,
+			"TFLAGS=" + jobsLFlagE,
 			"test-nonflaky",
 		},
 	},