Revert "component/python-mysqlclient: build with MariaDB Connector/C."

This reverts commit cd33366e.

MariaDB Connector/C 2.3.2 is broken. Here is strace output while running
test_max_allowed_packet from NEO test suite:

poll([{fd=4, events=POLLIN|POLLPRI}], 1, 0) = 0 (Timeout)
sendto(4, "\377\377\377\0\3SELECT 'xxxxxxxxxxxxxxxxxxx"..., 8192, MSG_DONTWAIT, NULL, 0) = 8192
sendto(4, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 16769027, MSG_DONTWAIT, NULL, 0) = 219264
sendto(4, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 16549763, MSG_DONTWAIT, NULL, 0) = 36544
sendto(4, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 16513219, MSG_DONTWAIT, NULL, 0) = -1 EAGAIN (Resource temporarily unavailable)
sendto(4, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 16513219, MSG_DONTWAIT, NULL, 0) = -1 EAGAIN (Resource temporarily unavailable)
sendto(4, "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"..., 16513219, MSG_DONTWAIT, NULL, 0) = -1 EAGAIN (Resource temporarily unavailable)
fcntl(4, F_SETFL, O_RDWR)               = 0
shutdown(4, SHUT_RDWR)                  = 0
close(4)                                = 0

mysqlclient does not build with the development branch of MariaDB Connector/C,
due to a missing 'my_config.h' file.

component/python-mysqlclient/buildout.cfg

@@ -8,7 +8,7 @@ parts =
   python-mysqlclient
 
 [python-mysqlclient-env]
-PATH =${mariadb-connector-c:location}/bin:%(PATH)s
+PATH =${mariadb:location}/bin:%(PATH)s
 
 [python-mysqlclient]
 recipe = zc.recipe.egg:custom
@@ -18,6 +18,6 @@ library-dirs =
   ${zlib:location}/lib/
   ${openssl:location}/lib/
 rpath =
-  ${mariadb-connector-c:location}/lib/mariadb
+  ${mariadb:location}/lib/
   ${zlib:location}/lib/
   ${openssl:location}/lib/