MIPS: Remove remnants of UASM_ISA

Commit 33679a50370d ("MIPS: uasm: Remove needless ISA abstraction")
removed use of the MIPS_ISA preprocessor macro, but left a couple of
unused definitions of it behind.

Remove the dead code.

Signed-off-by: Paul Burton <paul.burton@mips.com>

arch/mips/mm/uasm-micromips.c

@@ -19,7 +19,6 @@
 #include <asm/inst.h>
 #include <asm/elf.h>
 #include <asm/bugs.h>
-#define UASM_ISA	_UASM_ISA_MICROMIPS
 #include <asm/uasm.h>
 
 #define RS_MASK		0x1f

arch/mips/mm/uasm-mips.c

@@ -19,7 +19,6 @@
 #include <asm/inst.h>
 #include <asm/elf.h>
 #include <asm/bugs.h>
-#define UASM_ISA	_UASM_ISA_CLASSIC
 #include <asm/uasm.h>
 
 #define RS_MASK		0x1f