Remove conflicting legacy compose sequences in favour of X.org sequences

Remove conflicting legacy compose sequences in favour of X.org sequences

Patch by Jeroen Hoek. See bug 557420 for a prolonged discussion.
Quick summary of the removed sequences:

<Multi_key> <asciicircum> <0>
Consistency. <Multi_key> <asciicircum> [1..9] gives the superscript digit,
legacy sequence for zero is inconsistent.

<Multi_key> <c> <o>
<Multi_key> <c> <O>
Consistency. <Multi_key> <c> [:letter:] already gives vowel plus caron, legacy
sequence for c is inconsistent.

<Multi_key> <comma> <e>
<Multi_key> <comma> <E>
Consistency. <Multi_key> <comma> [:letter:] is for letter with cedilla,
<Multi_key> <semicolon> [:letter:] is for letter with ogolek

<Multi_key> <C> <slash>
<Multi_key> <slash> <C>
Unintuitive. ¢ is visually a vertical bar through a lowercase c, not a slash
through an uppercase C. ₡ has no alternatives, whilst ¢ can be typed as
<Multi_key> <bar> <c>.

<Multi_key> <d> <minus>
đ can be input through <Multi_key> <minus> <d>. <Multi_key> <d> <minus> is used
for ₫.

<Multi_key> <equal> <L>
<Multi_key> <L> <equal>
Unintuitive. ₤ has two dashes, £ one; therefore L + = > ₤, and L + - = £.

<Multi_key> <exclam> <s>
<Multi_key> <exclam> <S>
Consistency. <Multi_key> <exclam> [:letter:] is used for letter with dot below.
§ can be input using <Multi_key> <o> <s>.

<Multi_key> <period> <period>
Might need an alternative for ˙, but … (upstream) has no alternative either.

<Multi_key> <underscore> <a>
<Multi_key> <underscore> <A>
<Multi_key> <underscore> <o>
<Multi_key> <underscore> <O>
Consistency. <Multi_key> <underscore> [:vowel:] gives vowel with macron for ȳ ū
ī ē too.

<Multi_key> <minus> <d>
<Multi_key> <minus> <D>
<Multi_key> <o> <e>
<Multi_key> <O> <E>
Redundant. In upstream as is.