qcacld-3.0: Remove cds_context::dp_mem_pre_alloc_ctx

The dp_mem_pre_alloc_ctx was added to struct cds_context by the
following patch:
  qcacld-3.0: Add support to pre-allocate DP SRNG mem
  Change-Id I1f814f9f18d482eb5f55e0b157606d1792e665f8

However, that patch didn't actually use the member, and it hasn't been
used since, so remove it.

Change-Id: I8799e11cb753432b8433782990be6c259a785271
CRs-Fixed: 3428230

core/cds/inc/cds_sched.h

@@ -195,8 +195,6 @@ struct cds_context {
 
 	void *dp_soc;
 
-	void *dp_mem_pre_alloc_ctx;
-
 	/* Configuration handle used to get system configuration */
 	struct cdp_cfg *cfg_ctx;