Remove _mesa_memset in favor of plain memset.

This may break the SUNOS4 build, but it's no longer relevant.

src/mesa/main/renderbuffer.c

@@ -548,7 +548,7 @@ put_mono_row_ubyte3(GLcontext *ctx, struct gl_renderbuffer *rb, GLuint count,
    ASSERT(rb->DataType == GL_UNSIGNED_BYTE);
    if (!mask && val0 == val1 && val1 == val2) {
       /* optimized case */
-      _mesa_memset(dst, val0, 3 * count);
+      memset(dst, val0, 3 * count);
    }
    else {
       GLuint i;
@@ -1319,7 +1319,7 @@ put_mono_row_alpha8(GLcontext *ctx, struct gl_renderbuffer *arb, GLuint count,
       }
    }
    else {
-      _mesa_memset(dst, val, count);
+      memset(dst, val, count);
    }
 }