If libcrypto implementation of AES is used, do not compile internal

[TomasKorbar]

Hi,
this is somewhat cosmetic change. When libcrypto implementation of
AES is used, rijndael.cc file does not have to be compiled and linked
into the library. This allows us to not list rijndael AES implementation
as bundled feature of libmemcached in Fedora and RHEL package.

[codecov-commenter]

Codecov Report

Merging #122 (65a1489) into v1.x (6079c0e) will decrease coverage by 8%.
The diff coverage is n/a.

❗ Current head 65a1489 differs from pull request most recent head 0dc8017. Consider uploading reports for the commit 0dc8017 to get more accurate results

@@           Coverage Diff           @@
##            v1.x    #122     +/-   ##
=======================================
- Coverage     68%     61%     -8%     
=======================================
  Files        194     194             
  Lines      17478   15978   -1500     
=======================================
- Hits       11929    9704   -2225     
- Misses      5549    6274    +725     

Impacted Files	Coverage Δ
src/libmemcached/common.h	0% <0%> (-100%)	⬇️
src/libmemcached/csl/context.h	0% <0%> (-87%)	⬇️
src/libmemcached/memory.h	0% <0%> (-86%)	⬇️
test/lib/Server.hpp	0% <0%> (-77%)	⬇️
src/libmemcached/auto.cc	0% <0%> (-69%)	⬇️
src/libmemcached/options.cc	0% <0%> (-63%)	⬇️
src/libmemcached/behavior.cc	12% <0%> (-60%)	⬇️
test/lib/random.hpp	40% <0%> (-60%)	⬇️
src/libmemcached/namespace.cc	0% <0%> (-58%)	⬇️
src/libmemcached/sasl.cc	0% <0%> (-49%)	⬇️
... and 100 more

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