Removing MP4 encoding information
Use bitstream filter filter_units with ffmpeg 4.0 or newer.

ffmpeg -i INPUT -c copy -bsf:v 'filter_units=remove_types=6' OUTPUT


P.S.

/* NAL unit types */
enum {
    H264_NAL_SLICE           = 1,
    H264_NAL_DPA             = 2,
    H264_NAL_DPB             = 3,
    H264_NAL_DPC             = 4,
    H264_NAL_IDR_SLICE       = 5,
    H264_NAL_SEI             = 6,
    H264_NAL_SPS             = 7,
    H264_NAL_PPS             = 8,
    H264_NAL_AUD             = 9,
    H264_NAL_END_SEQUENCE    = 10,
    H264_NAL_END_STREAM      = 11,
    H264_NAL_FILLER_DATA     = 12,
    H264_NAL_SPS_EXT         = 13,
    H264_NAL_AUXILIARY_SLICE = 19,
};