freeradius3: Fix build when pcre is present

freeradius3: Fix build when pcre is present

If pcre is built before freeradius, then freeradius' configure will
detect pcre and freeradius will be built with pcre functionality
enabled. This causes a "missing dependencies" error at the end of
package build.

This passes --without-pcre to configure to disable this autodetection.

This also removes the dependency on libpcre2 as freeradius v3 does not
have support for pcre2.

Fixes: 19ec30255f13 ("freeradius3: switch to pcre2")
Fixes: https://github.com/openwrt/packages/issues/22574
Signed-off-by: Jeffery To <[email protected]>