Revert "Add MIPS64r6 support for libpixelflinger"

This reverts commit ab5265ebe65eac3b9555eaa3f425cf8e2759d3b3.

This broke the mips64 build (which, stupidly, I hadn't tested):

  system/core/libpixelflinger/codeflinger/MIPS64Assembler.h:24:35: fatal error: tinyutils/KeyedVector.h: No such file or directory
   #include "tinyutils/KeyedVector.h"

Change-Id: I4fa1c04e196592fd1ef893a83c75261a55d32290
diff --git a/libpixelflinger/codeflinger/MIPSAssembler.h b/libpixelflinger/codeflinger/MIPSAssembler.h
index 68a2b4f..430ab06 100644
--- a/libpixelflinger/codeflinger/MIPSAssembler.h
+++ b/libpixelflinger/codeflinger/MIPSAssembler.h
@@ -244,20 +244,20 @@
                 MIPSAssembler(const sp<Assembly>& assembly, ArmToMipsAssembler *parent);
     virtual     ~MIPSAssembler();
 
-    virtual uint32_t*   base() const;
-    virtual uint32_t*   pc() const;
-    virtual void        reset();
+    uint32_t*   base() const;
+    uint32_t*   pc() const;
+    void        reset();
 
-    virtual void        disassemble(const char* name);
+    void        disassemble(const char* name);
 
-    virtual void        prolog();
-    virtual void        epilog(uint32_t touched);
-    virtual int         generate(const char* name);
-    virtual void        comment(const char* string);
-    virtual void        label(const char* string);
+    void        prolog();
+    void        epilog(uint32_t touched);
+    int         generate(const char* name);
+    void        comment(const char* string);
+    void        label(const char* string);
 
     // valid only after generate() has been called
-    virtual uint32_t*   pcForLabel(const char* label);
+    uint32_t*   pcForLabel(const char* label);
 
 
     // ------------------------------------------------------------------------
@@ -399,9 +399,9 @@
 
 
 
-protected:
-    virtual void string_detab(char *s);
-    virtual void string_pad(char *s, int padded_len);
+private:
+    void string_detab(char *s);
+    void string_pad(char *s, int padded_len);
 
     ArmToMipsAssembler *mParent;
     sp<Assembly>    mAssembly;
@@ -537,11 +537,7 @@
 enum mips_regnames {
     R_zero = 0,
             R_at,   R_v0,   R_v1,   R_a0,   R_a1,   R_a2,   R_a3,
-#if __mips_isa_rev < 6
     R_t0,   R_t1,   R_t2,   R_t3,   R_t4,   R_t5,   R_t6,   R_t7,
-#else
-    R_a4,   R_a5,   R_a6,   R_a7,   R_t0,   R_t1,   R_t2,   R_t3,
-#endif
     R_s0,   R_s1,   R_s2,   R_s3,   R_s4,   R_s5,   R_s6,   R_s7,
     R_t8,   R_t9,   R_k0,   R_k1,   R_gp,   R_sp,   R_s8,   R_ra,
     R_lr = R_s8,