branch-3.0: [cleanup](load) remove bvar "g_memtable_input_block_allocated_size" #44304

[github-actions]

Cherry-picked from #44304

[doris-robot]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[doris-robot]

run buildall

[doris-robot]

TPC-H: Total hot run time: 40574 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit 15c195fb0216b9f90cfabfd084f36b03651539e0, data reload: false

------ Round 1 ----------------------------------
q1	17571	7422	7255	7255
q2	2070	167	159	159
q3	10708	1061	1148	1061
q4	10541	740	718	718
q5	7754	2834	2715	2715
q6	261	145	144	144
q7	974	623	593	593
q8	9571	1943	1955	1943
q9	8028	6424	6458	6424
q10	6956	2283	2300	2283
q11	455	263	265	263
q12	404	218	211	211
q13	17762	2979	2963	2963
q14	250	206	207	206
q15	553	517	526	517
q16	685	614	624	614
q17	970	647	610	610
q18	7215	6690	6539	6539
q19	2277	1080	1050	1050
q20	453	194	214	194
q21	4059	3249	3136	3136
q22	1058	988	976	976
Total cold run time: 110575 ms
Total hot run time: 40574 ms

----- Round 2, with runtime_filter_mode=off -----
q1	7331	7213	7312	7213
q2	319	228	233	228
q3	3039	2878	2852	2852
q4	2067	1725	1719	1719
q5	5667	5725	5772	5725
q6	224	139	140	139
q7	2208	1769	1743	1743
q8	3380	3457	3424	3424
q9	8874	8834	8836	8834
q10	3558	3487	3544	3487
q11	586	495	496	495
q12	811	625	597	597
q13	16468	3134	3180	3134
q14	287	267	274	267
q15	582	512	531	512
q16	716	664	660	660
q17	1848	1623	1609	1609
q18	8165	7855	7563	7563
q19	3795	1617	1530	1530
q20	2095	1870	1842	1842
q21	5487	5310	5223	5223
q22	1126	1028	1025	1025
Total cold run time: 78633 ms
Total hot run time: 59821 ms