Build: configure: Rework curses detection.

• Get rid of the large block in configure.ac in favor of using AC_SEARCH_LIBS.

• Rename CURSES_ENABLED to PCMK__ENABLE_CURSES.

• Simplify the block in crm_mon.h to only check for the right header to include. Whether or not to build with curses is entirely handled by configure.ac now.

• Rename CURSESLIBS to CURSES_LIBS for consistency.

• Get rid of PC_NAME_CURSES and PC_LIBS_CURSES, which aren't used anywhere.

• Get rid of HAVE_INCOMPATIBLE_PRINTW. Instead of having this duplicate flag, we can just set PCMK__ENABLE_CURSES based on this test.

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