[C++] Remove minPoolSize (#99)

* remove deprecated minPoolSize param

Author: rachel-mack

source/connect/connection-pools.txt

@@ -40,30 +40,11 @@ details on how to use a ``mongocxx::client`` in a thread-safe manner.
 Configuring a Connection Pool
 -----------------------------
 
-The number of clients in a connection pool is determined by the URI
-parameters ``minPoolSize`` and ``maxPoolSize``. The ``minPoolSize`` and
-``maxPoolSize`` options set resource usage targets for when the driver is
-idle or fully-utilized.  When fully utilized, up to maxPoolSize clients
-are available. When clients are returned to the pool, they are destroyed
-until the pool has shrunk again to the minPoolSize.
-
-.. list-table::
-   :header-rows: 0
-   :stub-columns: 1
-   :widths: 20 35
-
-   * - maxPoolSize
-     - The maximum number of clients created by a mongocxx::pool (both in the
-       pool and checked out). The default value is 100. Once it is reached,
-       mongocxx::pool::acquire blocks until another thread returns a client to
-       the pool.
-
-   * - minPoolSize
-     - Sets a target size for the pool when idle.  Once this many clients have
-       been created, there will never be fewer than this many clients in the
-       pool. If additional  clients above minPoolSize are created, they will be
-       destroyed when returned to the pool. The default value is "0", which
-       disables this feature. When disabled, clients are never destroyed.
+The number of clients in a connection pool is limited by the URI parameter
+``maxPoolSize``. After the number of clients created by a ``mongocxx::pool``
+(both in the pool and checked out) reaches the value of ``maxPoolSize``,
+``mongocxx::pool::acquire`` blocks until another thread returns a client to the
+pool. The default value is 100.
 
 Using a Connection Pool
 -----------------------