gdb/testsuite: Remove duplicates from gdb.base/solib-display.exp

When running the testsuite, I have:

    Running .../gdb/testsuite/gdb.base/solib-display.exp ...
    DUPLICATE: gdb.base/solib-display.exp: NO: break 25
    DUPLICATE: gdb.base/solib-display.exp: NO: continue
    DUPLICATE: gdb.base/solib-display.exp: IN: break 25
    DUPLICATE: gdb.base/solib-display.exp: IN: continue
    DUPLICATE: gdb.base/solib-display.exp: SEP: break 25
    DUPLICATE: gdb.base/solib-display.exp: SEP: continue

The 'break 25' appears because the test inserts two breakpoints at the
same location.  Fix this by only inserting the breakpoint once.

Fix the 'continue' DUPLICATE by giving a phony name to the second
continue: 'continue two'.

While at it, this commit also removes a trailing space.

Tested on x86_64-linux.