ITS#8977 - Remove documentation for idlexp

The idlexp feature depends on additional work that is not yet done. Remove documentation for the feature

doc/man/man5/slapd-mdb.5

@@ -17,18 +17,6 @@ primary database backend.
 The \fBmdb\fP backend uses a hierarchical database layout which
 supports subtree renames.
 .SH CONFIGURATION
-These
-.B slapd.conf
-options apply to the \fBmdb\fP backend.
-That is, they must follow a "backend mdb" line and
-come before any subsequent "backend" or "database" lines.
-.TP
-.BI idlexp \ <exp>
-Specify a power of 2 for the maximum size of an index slot.
-The default is 16, yielding a maximum slot size of 2^16 or 65536.
-Once set, this option applies to every \fBmdb\fP database instance.
-The specified value must be in the range of 16-31.
-.LP
 
 These
 .B slapd.conf