Remove hard-coded subdirectory paths for configs

Previously, the subdirectories in which the sub-json files were searched
in were hardcoded. Now, DRAMSys simply searches in the directory of the
base config, making this approach more flexible.

configs/traces/ranktest.stl

@@ -1,33 +0,0 @@
-0:	write	0x00000000
-1:	write	0x08000000
-2:	write	0x10000000
-3:	write	0x18000000
-4:	write	0x20000000
-5:	write	0x28000000
-6:	write	0x30000000
-7:	write	0x38000000  
-8:	write	0x40000000
-9:	write	0x48000000
-10:	write	0x50000000
-11:	write	0x58000000
-12:	write	0x60000000
-13:	write	0x68000000
-14:	write	0x70000000
-15: write   0x78000000
-16: write   0x80000000
-17: write   0x88000000
-18: write   0x90000000
-19: write   0x98000000
-20: write   0xA0000000
-21: write   0xA8000000
-22: write   0xB0000000
-23: write   0xB8000000
-24: write   0xC0000000
-25: write   0xC8000000
-26: write   0xD0000000
-27: write   0xD8000000
-28: write   0xE0000000
-29: write   0xE8000000
-30: write   0xF0000000
-31: write   0xF8000000
-32: write   0x00000000