oss-fuzz: Don't clean build directory
The OSS-Fuzz environment depends on files put into subdirectories of $WORK, e.g. when building using ASan ("--sanitizer=memory"). Rely on Meson reconfiguring the build directory instead of removing everything.
The OSS-Fuzz environment depends on files put into subdirectories of $WORK, e.g. when building using ASan ("--sanitizer=memory"). Rely on Meson reconfiguring the build directory instead of removing everything.