[Chore](thrift) prevent BE to be recompiled many files apache#19272

Prevent BE to be recompiled many files:

When we execute build.sh, it clean thrift code so that BE will be recompiled many files. It is added by this pr
apache#19217
We can use build.sh --clean to clean the thrift code. No need to clean it every time.

Author: ZhangYu0123

generated-source.sh

@@ -30,7 +30,6 @@ export DORIS_HOME="${ROOT}"
 
 echo "Build generated code"
 cd "${DORIS_HOME}/gensrc"
-rm -rf "${DORIS_HOME}/gensrc/build"
 # DO NOT using parallel make(-j) for gensrc
 make
 rm -rf "${DORIS_HOME}/fe/fe-common/src/main/java/org/apache/doris/thrift ${DORIS_HOME}/fe/fe-common/src/main/java/org/apache/parquet"