- use an array instead of a map for the schemes, as the overwhelming majority
of them will be either http or https, which we can place in front of the
array. This is faster than using a map.
- Simplify hasValidURIScheme by using strings.HasPrefix instead of doing
strings.IndexByte
- Simplify isBlockedResource by using a simple for loop, instead of a weird
slices.ContainsFunc+strings.Contains construct.
On my noisy system:
```
goos: linux
goarch: arm64
pkg: miniflux.app/v2/internal/reader/sanitizer
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
Sanitize-8 22.19m ± 4% 21.97m ± 4% ~ (p=0.948 n=50)
```
5a97bf8b5e