lib-sieve: sieve - Remove unused keep_r argument from execution functions.

src/lib-sieve/sieve.c

src/lib-sieve/sieve.h

src/plugins/imap-filter-sieve/imap-filter-sieve.c

src/plugins/imapsieve/imap-sieve.c

src/plugins/lda-sieve/lda-sieve-plugin.c

src/sieve-tools/sieve-filter.c

src/sieve-tools/sieve-test.c

src/testsuite/testsuite-script.c