Update build procedure for gf180mcu and sky130 according to latest open_pdks

[kareefardi]

common:

+ generate --disable<scl/lib> similar to --enable since almost everything is enabled by default now

sky130:

+ add LIB_FLAG_MAP similar to gf180mcu
~ treat sram as a any other lib now
- remove `sources` folder from open_pdks to save space if build finishes successfully
- remove cloning skywater-pdk

* This could be wrapped as an option although I don't see a reason for keeping sources folder after the build is successful.