Fix missing cleanup of trans.zstream #353

Job	Run time
build (plain linux, 1)	1m 8s
build (multi binary, 1, 1)	1m 1s
build (multi binary, dropbearmulti argv0, 1, 1)	1m 4s
build (client only, no, PROGRAMS=dbclient)	2m 25s
build (server only, no, PROGRAMS=dropbear)	27s
build (bundled libtom, bionic , no writev(), ubuntu-20.04, --enable-bundled-libtom --enable-werro...	33s
build (linux clang, clang)	2m 21s
build (c89, -std=c89 -Wdeclaration-after-statement, 1, --enable-pam, #define DROPBEAR_SNTRUP761 0 )	1m 3s
build (macos 14, macos-14, clang, -Wno-deprecated-declarations -Wno-undef, no, no, ranlib -no_war...	25s
build (macos 15, macos-15, clang, -Wno-deprecated-declarations -Wno-undef, no, no, ranlib -no_war...	39s
build (DEBUG_TRACE, 1, --enable-pam, #define DEBUG_TRACE 5 )	1m 49s
build (nondefault options, 1, --enable-pam)	1m 5s
build (most options disabled, --disable-harden --disable-zlib --disable-openpty --disable-lastlog...	30s
build (no sha1, no, #define DROPBEAR_SHA1_HMAC 0 #define DROPBEAR_RSA_SHA1 0 #define DROPBEAR_DH_...	1m 13s
build (pq, no plain x25519, #define DROPBEAR_CURVE25519 0 )	1m 7s
	16m 50s

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