perlapi: Consolidate CopLABEL* entries

Making these a single entry makes perlapi more concise.

Author: khwilliamson

cop.h

@@ -636,19 +636,17 @@ be zero.
     cophh_2hv(CopHINTHASH_get(cop), flags)
 
 /*
-=for apidoc Am|const char *|CopLABEL|COP *const cop
+=for apidoc   Am|const char *|CopLABEL          |COP *const cop
+=for apidoc_item|const char *|CopLABEL_len      |COP *const cop|STRLEN *len
+=for apidoc_item|const char *|CopLABEL_len_flags|COP *const cop|STRLEN *len|U32 *flags
 
-Returns the label attached to a cop.
+These return the label attached to a cop.
 
-=for apidoc Am|const char *|CopLABEL_len|COP *const cop|STRLEN *len
+C<CopLABEL_len> and C<CopLABEL_len_flags> additionally store the number of
+bytes comprising the returned label into C<*len>.
 
-Returns the label attached to a cop, and stores its length in bytes into
-C<*len>.
-
-=for apidoc Am|const char *|CopLABEL_len_flags|COP *const cop|STRLEN *len|U32 *flags
-
-Returns the label attached to a cop, and stores its length in bytes into
-C<*len>.  Upon return, C<*flags> will be set to either C<SVf_UTF8> or 0.
+C<CopLABEL_len_flags> additionally returns the UTF-8ness of the returned label,
+by setting C<*flags> to 0 or C<SVf_UTF8>.
 
 =cut
 */