[infra] flattening base-clang image
[infra] flattening base-clang image

The image has lots of layers with lots of deleted files (sources and intermediates).
Flatten the image to reduce its size.
robertswiecki/oss-fuzz,googlefonts/oss-fuzz,vitalybuka/oss-fuzz,googlefonts/oss-fuzz,kcc/oss-fuzz,vitalybuka/oss-fuzz,googlefonts/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,oliverchang/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,googlefonts/oss-fuzz,googlefonts/oss-fuzz,googlefonts/oss-fuzz,vitalybuka/oss-fuzz,robertswiecki/oss-fuzz,skia-dev/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,ssbr/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,ssbr/oss-fuzz,ssbr/oss-fuzz,kcc/oss-fuzz,robertswiecki/oss-fuzz,vitalybuka/oss-fuzz,skia-dev/oss-fuzz,kcc/oss-fuzz,oliverchang/oss-fuzz,skia-dev/oss-fuzz,oliverchang/oss-fuzz,oliverchang/oss-fuzz,skia-dev/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,googlefonts/oss-fuzz,google/oss-fuzz,ssbr/oss-fuzz,kcc/oss-fuzz,vitalybuka/oss-fuzz,skia-dev/oss-fuzz,robertswiecki/oss-fuzz,robertswiecki/oss-fuzz,kcc/oss-fuzz,skia-dev/oss-fuzz,robertswiecki/oss-fuzz,skia-dev/oss-fuzz,FeliciaLim/oss-fuzz,google/oss-fuzz,google/oss-fuzz,google/oss-fuzz,robertswiecki/oss-fuzz,skia-dev/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,google/oss-fuzz,google/oss-fuzz,google/oss-fuzz,FeliciaLim/oss-fuzz,skia-dev/oss-fuzz,googlefonts/oss-fuzz,robertswiecki/oss-fuzz,googlefonts/oss-fuzz,ssbr/oss-fuzz,skia-dev/oss-fuzz,oliverchang/oss-fuzz