intel/fs: Get rid of fs_inst::equals

There are piles of fields that it doesn't check so using it is a lie.
The only reason why it's not causing problem is because it has exactly
one user which only uses it for MOV instructions (which aren't very
interesting) and only on Sandy Bridge and earlier hardware.  Just get
rid of it and inline it in the one place that it's actually used.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

src/intel/compiler/brw_ir_fs.h

@@ -347,7 +347,6 @@ public:
 
    void resize_sources(uint8_t num_sources);
 
-   bool equals(fs_inst *inst) const;
    bool is_send_from_grf() const;
    bool is_partial_write() const;
    bool is_copy_payload(const brw::simple_allocator &grf_alloc) const;