INNODB_ZIP and INNODB_ZIP_RESET to
INNODB_COMPRESSION and INNODB_COMPRESSION_RESET,
and remove the statistics of the buddy system.

This change was discussed with Ken.  It makes the tables shorter
and easier to understand.  The removed data will be represented in
the tables INNODB_COMPRESSION_BUDDY and INNODB_COMPRESSION_BUDDY_RESET
that will be added later.

i_s_innodb_zip, i_s_innodb_zip_reset, i_s_zip_fields_info[],
i_s_zip_fill_low(), i_s_zip_fill(), i_s_zip_reset_fill(),
i_s_zip_init(), i_s_zip_reset_init(): Replace "zip" with "compression".

i_s_compression_fields_info[]: Remove "used", "free",
"relocated", "relocated_usec".  In "compressed_usec" and "decompressed_usec",
replace microseconds with seconds ("usec" with "sec").

page_zip_decompress(): Correct a typo in the function comment.

PAGE_ZIP_SSIZE_BITS, PAGE_ZIP_NUM_SSIZE: New constants.

page_zip_stat_t, page_zip_stat: Statistics of the compression, grouped
by page size.

page_zip_simple_validate(): Assert that page_zip->ssize is reasonable.