Remove stale .clang-tidy entries

-google-runtime-references disabled a check that neither clang-tidy
22.1.8 nor 23.1.2 lists under --list-checks -checks='*'; it was
removed upstream. The commented-out HeaderFilterRegex line has been
unused since the active HeaderFilterRegex was introduced in #2561
(2021).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

#5725 item 11

.clang-tidy

@@ -43,7 +43,6 @@ Checks: '*,
          -google-readability-function-size,
          -google-runtime-float,
          -google-runtime-int,
-         -google-runtime-references,
          -hicpp-avoid-goto,
          -hicpp-explicit-conversions,
          -hicpp-function-size,
@@ -87,5 +86,4 @@ CheckOptions:
 
 WarningsAsErrors: '*'
 
-#HeaderFilterRegex: '.*nlohmann.*'
 HeaderFilterRegex: '.*hpp$'