Fixing build-bot compilation failure on SolarisX86,

who has two different incompatible copies of zlib installed:
(in /usr and in /usr/local).
cmake errorneously chose *.h file from /usr/local/include,
while zlib.a/zlib.so from /usr/lib/. Compilation failed
because of a missing symbol gzopen64.

modified:
  @ cmake/zlib.cmake
  Removing the line (as suggested by Vlad) which made cmake choose
  the wrong library.
  Note: this line used to be a hack for old HP machines,
  it's not needed anymore.

cmake/zlib.cmake

@@ -58,7 +58,6 @@ MACRO (MYSQL_CHECK_ZLIB_WITH_COMPRESS)
       CHECK_FUNCTION_EXISTS(crc32 HAVE_CRC32)
       SET(CMAKE_REQUIRED_LIBRARIES)
       IF(HAVE_CRC32)
-        SET(ZLIB_LIBRARY z CACHE INTERNAL "System zlib library")
         SET(WITH_ZLIB "system" CACHE STRING "Which zlib to use (possible values are 'bundled' or 'system')")
         SET(ZLIB_SOURCES "")
       ELSE()