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.
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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.