[chore][internal/filterset] Remove outdated and incorrect comment (op…

…en-telemetry#30259)

**Description:**
This comment was added with the original introduction of this component,
but the functionality it's referencing was removed shortly thereafter
(intentionally from what I can tell), and has no longer been in place
for 3+ years.

**Link to tracking Issue:** <Issue number if applicable>
Resolves open-telemetry#30178

internal/filter/filterset/regexp/regexpfilterset.go

@@ -73,7 +73,6 @@ func (rfs *FilterSet) Matches(toMatch string) bool {
 }
 
 // addFilters compiles all the given filters and stores them as regexes.
-// All regexes are automatically anchored to enforce full string matches.
 func (rfs *FilterSet) addFilters(filters []string) error {
 	dedup := make(map[string]struct{}, len(filters))
 	for _, f := range filters {