Drop Database without Database Configuration Assistance (DBCA)

$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Mon Oct 3 15:47:23 2016

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Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> shutdown abort
ORACLE instance shut down.
SQL> startup mount exclusive restrict;
ORACLE instance started.

Total System Global Area 1.2827E+10 bytes
Fixed Size                  2258352 bytes
Variable Size            7046433360 bytes
Database Buffers         5771362304 bytes
Redo Buffers                7315456 bytes
Database mounted.

SQL> drop database;

Database dropped.

SQL> exit