fuzz: remove some chunk identifiers from stb_png.dict

these chunks are not parsed

tests/stb_png.dict

@@ -5,26 +5,4 @@ section_iend="IEND"
 section_ihdr="IHDR"
 section_plte="PLTE"
 section_trns="tRNS"
-section_chrm="cHRM"
-section_gama="gAMA"
-section_iccp="iCCP"
-section_sbit="sBIT"
-section_srgb="sRGB"
-section_text="tEXt"
-section_ztxt="zTXt"
-section_itxt="iTXt"
-section_bkgd="bKGD"
-section_hist="hIST"
-section_phys="pHYs"
-section_splt="sPLT"
-section_time="tIME"
-section_offs="oFFs"
-section_exif="eXIf"
-section_frac="fRAc"
-section_pcal="pCAL"
-section_scal="sCAL"
-section_ster="sTER"
-section_gifg="gIFg"
-section_gift="gIFt"
-section_gifx="gIFx"
 section_cgbi="CgBI"