profiler: remove PprofDiff (#2267)

We deprecated PprofDiff in v1.49.0, with a note that it would be removed
in a future release. There is a low likelihood that any user actually
depends on this, and at any rate we have had several releases during
which time staticcheck/other linters could flag the deprecated function.
Finally remove it and inline it into the one place it was used.

profiler/profile.go

@@ -389,22 +389,6 @@ func (fdp *fastDeltaProfiler) Delta(data []byte) (b []byte, err error) {
 	return b, nil
 }
 
-// PprofDiff computes the delta between all values b-a and returns them as a new
-// profile. Samples that end up with a delta of 0 are dropped. WARNING: Profile
-// a will be mutated by this function. You should pass a copy if that's
-// undesirable.
-//
-// Deprecated: This function was introduced into our public API unintentionally.
-// It will be removed in the next release. If you need this functionality,
-// it can be implemented in two lines:
-//
-//	a.Scale(-1)
-//	return pprofile.Merge([]*pprofile.Profile{a, b})
-func PprofDiff(a, b *pprofile.Profile) (*pprofile.Profile, error) {
-	a.Scale(-1)
-	return pprofile.Merge([]*pprofile.Profile{a, b})
-}
-
 func goroutineDebug2ToPprof(r io.Reader, w io.Writer, t time.Time) (err error) {
 	// gostackparse.Parse() has been extensively tested and should not crash
 	// under any circumstances, but we really want to avoid crashing a customers

profiler/profile_test.go

@@ -418,7 +418,8 @@ func requirePprofEqual(t *testing.T, a, b []byte) {
 	require.NoError(t, err)
 	pprofB, err := pprofile.ParseData(b)
 	require.NoError(t, err)
-	pprofDiff, err := PprofDiff(pprofA, pprofB)
+	pprofA.Scale(-1)
+	pprofDiff, err := pprofile.Merge([]*pprofile.Profile{pprofA, pprofB})
 	require.NoError(t, err)
 	require.Len(t, pprofDiff.Sample, 0)
 }