Fix clang-tidy readability-isolate-declaration warnings

I missed one of these in review so a machine is probably better at
catching them.

I fixed the existing instances which where largely in code which look
dated. Where possible I slightly reorganized the code so we do not have
to leave values uninitialized, but did not touch up anything else.

src/util.cc

@@ -1335,7 +1335,6 @@ char* uitoa_n(uint64_t value, char* str, int n, int base, const char* prefix) {
 
     int i = 0;
     uint64_t v;
-    char *p, *q;
     char c;
 
     if ( prefix ) {